GIFT   OF 
PROP.   W  R 


/I. 


ELECTRCCHEMICAL 
ANALYSIS. 


BY 

EDGAR  F.  SMITH, 

^  I 

PROFESSOR    OF   CHEMISTRY,    UNIVERSITY    OF    PENNSYLVANIA. 


THIRD    EDITION,   REVISED   AND    ENLARGED. 


1Wustratton0. 


PHILADELPHIA: 

P.    BLAKISTON'S   SON   &  CO., 

1012   WALNUT   STREET. 
IQ02. 


15 


Copyright,  1902,  by  P.  BLAKISTON'S  SON  &  Co. 


PRESS  OF  WM.  F.  FELL  A  CO.. 

1220-24  SANSOM  STREET, 

PHILADELPHIA. 


PREFACE. 


The  first  edition  of  this  book  appeared  twelve  years 
ago  (1890).  It  was  published  then  because  the  writer, 
after  many  years  of  experimentation,  was  convinced 
that  the  electric  current  had  proved  its  right  to  be  classed 
as  a  reagent  in  the  quantitative  determination  and 
separation  of  metals.  To-day  the  number  of  text-books 
relating  to  electro-chemical  analysis,  to  the  preparation 
of  inorganic  and  organic  compounds  in  the  electrolytic 
way,  and  to  the  various  theories  of  electrolysis  has  be- 
come quite  large.  There  is  scarcely  a  laboratory,  where 
chemical  analysis  is  taught,  or  where  it  is  applied,  in 
which  use  is  not  made  of  the  " subtile  agent"  of 
Faraday. 

Since  the  appearance  (1894)  of  the  second  edition,  as 
well  as  its  German  (1895)  and  French  (1900)  transla- 
tions, numerous  additions  have  been  made  to  the  domain 
of  which  the  book  especially  treats;  so  that  it  was  con- 
cluded to  thoroughly  revise  the  entire  text.  In  doing 
this  the  author  has  abstained  from  any  attempt  to 
present  the  prevalent  theories  on  electrolysis,  the  purpose 
of  the  book  being  of  a  wholly  different  character,  and, 
furthermore,  because  these  theories  have  been  ex- 
haustively treated  in  a  masterly  manner  in  special 
volumes  readily  accessible  to  all  students  of  chemistry. 

The  present  edition  differs  greatly  from  its  predecessors. 
Among  the  very  first  changes  will  be  observed  the  de- 

v 

237329 


VI  PREFACE. 

scription  of  an  electro-chemical  laboratory.  This  labora- 
tory has  been  the  outgrowth  of  a  real  demand  and  cannot 
fail  to  be  suggestive  and  perhaps  helpful  to  persons  who 
purpose  making  an  installation  for  electrolytic  work.  A 
few  alterations  have  been  made  in  the  historical  section, 
but  the  great  changes  will  appear  in  the  sections  devoted 
to  the  determination  and  separation  of  the  metals.  Many 
of  the  earlier  directions  in  reference  to  the  determination 
of  the  individual  metals  have  been  omitted  and  more 
reliable  and  definite  conditions  substituted  for  the  same. 
The  section  devoted  to  separations  has  been  entirely 
recast,  each  separation  being  given  in  all  of  its  possible 
forms  with  conditions  that  experience  has  demonstrated 
will  yield  satisfactory  results. 

The  new  illustrations  scattered  here  and  there  through 
the  text  have  been  made  from  photographs  taken  by 
Mr.  Walter  T.  Taggart,  Sc.B.,  to  whom  the  author's 
thanks  are  here  expressed.  It  is  also  a  great  pleasure 
to  acknowledge  indebtedness  to  the  many  students  who, 
through  a  period  of  years,  have  with  readiness  and  skill 
tested  methods  of  determination  and  separation,  time 
after  time,  as  the  writer  has  suggested. 

S. 

THE  JOHN  HARRISON  LABORATORY 

OF  CHEMISTRY. 

1902. 


TABLE  OF  CONTENTS. 


PAGE 

INTRODUCTION, 9-10 

ACTION  OF  THE  ELECTRIC  CURKENT  UPON  ACIDS  AND  SALTS,  .    .    .  10-13 

OHM,  VOLT,  AMPERE,       I3~14 

SOURCES  OF  ELECTRIC  CURRENT — 

Grenet  Battery,  Leclanche  Cell,  Daniell  Cell,  Meidinger  Cell, 
Crowfoot  Cell,  Bunsen  and  Grove  Batteiies,  Cupron  Cell, 
Magneto-electric  Machines,  Thermopile,  Storage  Cells,  The 

Electric-light  Current  in  Electrolysis, 14-28 

REDUCTION  OF  THE  CURRENT — 

Rheostats,  Resistance  Frame, 28-32 

MEASURING  CURRENT — 

Voltameter,  Amperemeter,  An  Electro-chemical    Laboratory,     .  32-44 

HISTORICAL  SKETCH, 44-58 

SPECIAL  PART. 

1.  DETERMINATIONS  OF  METALS, 58-120 

2.  SEPARATION  OF  METALS, 120-193 

3.  DETERMINATION  OF  THE  HALOGENS  IN  THE  ELECTROLYTIC  WAY,  193-194 

4.  DETERMINATION  OF  NITRIC  ACID  BY  ELECTROLYSIS, 194 

5.  OXIDATIONS  BY  MEANS  OF  THE  ELECTRIC  CURRENT, 194-199 

INDEX, 201 


vn 


ABBREVIATIONS. 


AM.  CH 

AM.  CH.  JR 

AM.  JR.  Sc.  AND  AR. 
AM.  PHIL.  Soc.    PR. 

ANN 

BER 

BERG-HUTT.    Z.        .     . 

B.  s.  CH.  PARIS     . 

CH.  NEWS 

CH.  Z 

C.  R 

DING.  P.  JR.       ... 
ELEKTROCH.  Z.      .    . 

G.  CH.  ITAL 

JAHRB 

J.  AM.  CH.  S.     .    .    . 

JR.  AN.  CH 

JR.  F.  PKT.  CH.     .    . 

JR.  FR.  INS 

M.  F.  CH 

PHIL.  MAG 

\VIED.  ANN 

Z.  F.  A.  CH 

Z.  F.  ANG.  CH.   .    .    . 

Z.  F.  ANORG.   CH.    .     . 

Z.  F.  ELEKTROCH  EM. 
Z.  F.  PH.  CH. 


The  American  Chemist. 

American  Chemical  Journal. 

American  Journal  of  Science  and  Arts. 

Proceedings  of  the  American   Philosophical  Society 

Annalen  der  Chemie  und  Pharmacie. 

Berichte  der  deutschen  chemischen   Gesellschaft. 

Berg-  und  Huttenmdnnische  Zeitung. 

Bulletin  de  la  Societe  Chimique  de  Paris. 

Chemical  Areivs. 

Chemiker-Zeitung. 

Comptes  Rendus. 

Dingier* s  Polylechnisches  Journal. 

Elektrochemische  Zeitschrift. 

Gazetta  chimica  italiana. 

JaJiresbericJit  der  Chemie. 

Journal  of  the  American  Chemical  Society. 

Journal  of  Analytical  and  Applied  Chemistry. 

Journal  fiir praktiscJie  Chemie. 

Journal  of  the  Franklin  Institute,  Phila. 

Monatsheft  fiir  Chemie. 

Philosophical  Magazine. 

IViedemann 's  Annalen. 

Zeitschrift  fur  analytische  Chemie. 

ZeitscJirift  fur  angewandte  Chemie. 

Zeitschrift  fiir  anorganische  Chemie. 

Zeitschrift  fur  Elektrochemie. 

Zeitschrift  fiir  physikalische  Chemie. 


Vlll 


ELECTRO-CHEMICAL 
ANALYSIS. 


INTRODUCTION. 

Many  chemical  compounds  are  decomposed  when  ex- 
posed to  the  action  of  an  electric  current.  A  decomposi- 
tion of  this  kind  is  called  electrolysis,  while  the  substance 
undergoing  change  is  termed  an  electrolyte.  The  products 
of  the  decomposition  are  the  anions  and  cathions,  or  those 
( i )  which  separate  at  the  anode,  the  positive  electrode  or 
pole  (-[-  P),  and  (2)  those  separating  at  the  cathode,  the 
negative  electrode  or  pole  ( —  P)  of  the  source  of  the  elec- 
tric energy. 

This  behavior  of  compounds  has  become  of  great  service 
to  the  analyst,  inasmuch  as  it  has  enabled  him  to  effect 
the  isolation  of  metals  from  their  solutions,  and  by  care- 
fully studying  the  electrolytic  behavior  of  salts  it  has  been 
possible  for  him  to  bring  about  quantitative  determina- 
tions and  separations. 

The  electrolytic  method  of  analysis  is  especially  in- 
viting, since  it  permits  of  clean,  accurate,  and  rapid  deter- 
minations where  the  ordinary  methods  yield  unsatis- 
factory results.  This  statement  is  readily  confirmed  on 
recalling  the  gravimetric  methods  usually  employed  in 
the  estimation  of  copper,  mercury,  cadmium,  bismuth, 
tin,  etc.,  etc.  That  this  assertion  may  be  the  conviction 

2  9 


IO  ELECTRO-CHEMICAL   ANALYSIS. 

of  every  student  of  analysis,  the  writer  would  call  atten- 
tion, first,  to  the  course  of  the  current  in  solutions  of  some 
of  the  more  frequently  occurring  salts;  after  which  will 
follow  a  brief  account  of  the  various  modes  of  obtaining 
the  electric  current,  how  it  may  be  measured,  and  how  con- 
trolled. Finally,  all  the  metals  which  have  been  studied 
electrolytically  will  be  taken  up  in  detail,  and  their  various 
determinations  will  be  followed  by  a  number  of  separa- 
tions to  show  how  widely  the  electrolytic  method  of  analy- 
sis may  be  applied. 

i.  ACTION   OF  THE  ELECTRIC  CURRENT  UPON 
ACIDS  AND   SALTS. 

At  the  At  the 

—  Pole.  +  Pole. 

Hydrochloric  acid  -f-  the  current  =  Hydrogen  -f-  Chlorine. 
Copper  chloride      +    "         "       =  Cu  -f  C12. 

Zinc  chloride          -f    "         "         =  Zn  +  C12. 

Nitric  acid  -f    "          «         =  H  +  NO2  -f  O. 

In  this  last  case  the  hydrogen  further  acts  upon  more 
nitric  acid  and  produces  ammonia  (NH3)  and  water. 

Lead  nitrate  -J-  the  current  =  Pb  -f  NO2  4-  O. 

The  oxygen  liberated  here  attacks  a  second  molecule 
of  lead  nitrate,  and  produces  lead  peroxide,  Pb(NO3)2  -f 
O2  =  PbO2,  which  deposits  upon  the  positive  electrode. 

At  the       At  the 
—  Pole.      +  Pole. 

Copper  nitrate  -j-  the  current  =  Cu  -j-  (NOS)2. 
Sulphuric  acid  -f  "         "       =  H2  -f-  SO4. 

Secondary  changes  frequently  occur  in  these  decom- 
positions; thus,  in  the  last  example  the  SO4  reacts  with 
the  water  present:  SO4  -f  H2O  =  H2SO4  -f  O,  the  oxygen 
going  to  the  positive  electrode.  In  the  electrolysis  of 


ACTION    OF    CURRENT    UPON    ACIDS    AND    SALTS.         I  I 

copper  sulphate,  which  is  analogous  to  sulphuric  acid, 
secondary  changes  also  occur. 

At  the    At  the 
—  Pole.  +  Pole. 

Potassium  sulphate  -f-  tne  current  =  K2  -f-  SO4. 

In  this  decomposition  the  liberated  potassium  acts  upon 
water,  with  the  liberation  of  hydrogen  and  the  formation 
of  potassium  hydroxide. 

Bourgoin  observed  the  following  changes  with  formic, 
acetic,  and  oxalic  acids,  and  their  salts : — 

1.  Formic  Acid. — The  decomposition  may  be  expressed 
in  two  equations — 

(a)  CH2O2  H      +  (CHO  +  O). 

—  Pole.  +  Pole. 

(b]  2(CHO  -f  O)  =  CH202  +  CO2. 

The  decomposition  of  sodium  formate  yields  carbon 
dioxide  and  formic  acid  at  the  anode,  and  hydrogen  and 
sodium  hydroxide  at  the  cathode. 

2.  Acetic  Acid. — The   electrolysis   of  the   dilute  acid 
affords  hydrogen  at  the  negative  electrode,  and  at  the 
positive  electrode  a  mixture  of  oxygen,  carbon  dioxide, 
and  a  small  quantity  of  carbon  monoxide.      Consult  also 
Z.  f.  ph.  Ch.,  33,  108. 

3.  Oxalic  Acid. — The  electrolysis  of  this  acid  with  a 
current  obtained  from  four  Bunsen  cells  gave  decompo- 
sitions which  may  be  expressed  as  follows  :— 

C2H2O4.2H2O  +  current  =  3H2  -f  2CO2  -f  O2; 
—  Pole.     +  Pole. 

the  oxygen  reacts  upon  additional  acid : — 

2C2H2O4  -f  2H2O  -f  O2  =  4CO2  -f  4H2O, 

so  that  the  final  products  are  pure  carbon  dioxide  at  the 
positive  electrode  and  hydrogen  at  the  opposite  pole. 


12  ELECTRO-CHEMICAL   ANALYSIS. 

The  decomposition  of  potassium  oxalate  may  be  formu- 
lated in  the  following  way  :  — 


the  liberated  metal  and  the  carbon  dioxide  then  react 
further  :  — 

2H2O  +  K2  =  2KOH  +  H2  and  2CO2  +  2KOH  =  2KHCO3. 

When  exposed  to  the  same  influence  ammonium  oxalate 
yields  hydrogen  at  the  negative  electrode,  and  hydrogen 
ammonium  carbonate  at  the  positive  electrode.  The 
latter  compound  further  breaks  down  into  ammonia  and 
carbon  dioxide. 

Succinic  acid  is  electrolyzed  with  difficulty.  In  its  de- 
composition the  products  which  have  generally  been  ob- 
served at  the  positive  electrode  were  oxygen  and  the  two 
oxides  of  carbon.  Its  electrolytic  oxidation  in  a  divided 
cell  gave  as  products  :  tartaric  acid,  oxalic  acid,  aromatic 
bodies,  oxygen,  carbon  monoxide,  carbon  dioxide,  ethy- 
lene  and  methane  (J.  Am.  Ch.  $.,  21,  967).  By  electro- 
lyzing  sodium  succinate  Kekule  obtained  hydrogen  at  the 
cathode,  and  carbon  dioxide  and  ethylene  at  the  anode. 

Tartaric  acid  -f  the  current  gave  at 

-  Pole.  -f  Pole. 

hydrogen  acetic    acid,    carbon    dioxide, 

carbon  monoxide,  and  oxygen; 

while  with  potassium  tartrate  the  products  were  hydrogen 
and  potassium  at  the  cathode  and  acid  potassium  tar- 
trate, carbon  dioxide,  carbon  monoxide,  and  oxygen  at 
the  anode.  An  alkaline  solution  of  potassium  tartrate 
gave  hydrogen  at  the  cathode  and  at  the  anode,  acetic 
acid,  the  oxides  of  carbon,  oxygen,  and  ethane  (C2H6). 
In  the  case  of  potassium  cyanide  the  products  are  potas- 


OHM,    VOLT,    AND    AMPERE.  13 

sium  hydroxide  and  hydrogen  at  the  cathode  with  cyano- 
gen at  the  anode.  The  cyanogen  does  not  appear  there 
in  gas  form,  but  as  an  isomeride,  paracyanogen.  As  the 
quantity  of  the  latter  increases,  the  liquid,  surrounding 
the  anode,  acquires  a  yellow  to  brownish-yellow  color. 
The  paracyanogen  separates  from  this  apparent  solution 
spontaneously  in  black,  amorphous  floccules.  (Hittorf, 
Z.  f.  ph.  Ch.,  10,  616;  also  12,  97.)  Also  consult  page  53. 
The  above  examples  will  suffice  to  indicate  the  nature 
of  the  decomposition  due  to  the  current;  they  will  assist 
very  materially  in  understanding  the  changes  occurring  in 
ordinary  electrolytic  analyses.  For  further  particulars  in 
this  direction,  consult  Tommasi's  Traite  Theorique  et 
pratique  d'Electrochimie,  although  the  statements  there 
made  will  in  many  instances  require  revision  in  the  light 
of  more  recent  investigations. 


2.   OHM,   VOLT,   AND  AMPERE. 

These  terms  may  be  defined  as  follows  :— 

The  ohm  is  the  unit  of  resistance.  Its  value  is  repre- 
sented by  a  column  of  mercury  i  sq.  mm.  in  cross-section, 
and  106.2  cm.  in  length  at  the  temperature  o°  C. 

The  volt  is  the  unit  of  electromotive  force  (B.  M.  F.). 
It  is  the  E.  M.  F.  which  gives  a  current  of  one  ampere 
through  a  resistance  of  one  ohm. 

The  ampere  is  the  unit  of  current.  It  is  the  current 
which,  under  an  electromotive  force  of  one  volt,  flows 
through  a  circuit  offering  a  resistance  of  one  ohm. 

V  E 

A  ~    — ;  or  better,  C         — . 
O  R 


14  ELECTRO-CHEMICAL    ANALYSIS. 

3.   SOURCES   OF  THE   ELECTRIC   CURRENT. 

The  electric  energy  required  for  quantitative  analysis 
has  been  variously  furnished  by  batteries  of  well-known 
types,  magneto-electric  machines,  dynamos,  thermopiles, 
and  electrical  accumulators  or  storage  cells.  A  brief 
description  of  some  of  these  may  be  properly  introduced 
here. 

The  Grenet  cell  or  Bichromate  Battery  (Fig.  i )  consists  of 
two  plates  of  carbon  (K)  and  one  of  zinc  (Z),  movable  by 

FIG.   i. 


means  of  the  handle,  a.  This  is  a  convenient  arrange- 
ment, as  it  allows  of  easy  interruption  of  the  current. 
The  liquid  to  be  used  in  this  cell  consists  of  potassium 
bichromate  (i  lb.),  strong  sulphuric  acid  (2  Ibs.),  and 
water  (12  Ibs.).  In  mixing  these,  the  probable  chemical 
change  is : — 

K2Cr207  +  7H2S04  =  2CrO3  +  K2SO4  +  H2O  +  6H2SO4. 


SOURCES   OF   THE    ELECTRIC    CURRENT. 


The  chemical  action  in  the  cell,  when  the  current  passes, 
may  be  expressed  by  the  equation  :— 


2Cr03  +  6H2S04  +  3Zn  =  Crs(SO4), 


6H2O. 


The  writer  found  four  cells  of  this  type  (capacity  two 
quarts)  very  serviceable  in  the  electrolysis  of  solutions  of 
cadmium,  uranium,  molybdenum,  and  other  metals.  No 
disagreeable  fumes  arise  from  cells  of  this  class.  The 


FIG.   3. 


electromotive  force  is  about  two  volts,  and  the  internal 
resistance  low.  The  Grenet  cell  loses  in  intensity  when 
used  for  long  periods,  but  regains  its  value  when  it  has 
remained  out  of  action  for  some  time. 

Leclanche  Cell  (Figs.  2  and  3). — Two  forms  of  this  cell 
are  in  use.  In  the  first,  to  the  left  of  the  figure,  there  is 
a  zinc  rod,  immersed  in  a  solution  of  ammonium  chloride, 
and  a  carbon  plate  inside  a  porous  cup,  tightly  packed 
with  a  mixture  of  manganese  dioxide  and  broken  gas 
carbon.  The  porous  cup  is  only  intended  to  hold  the 


I  6  ELECTRO-CHEMICAL    ANALYSIS. 

mixture  in  position.  There  is  but  one  liquid,  and  that  a 
strong  solution  of  ammonium  chloride.  The  E.  M.  F.  of 
this  cell  equals  1.47  volts;  it  decreases  rapidly  when  send- 
ing strong  currents.  It  is  inferior  to  the  Daniell  cell  when 
a  steady  current  is  desired  for  a  long  period. 

The  chemical  action  in  cells  of  this  kind  Ayrton  ex- 
presses as  follows: — 

(Before  sending  the  current) — 

k  C  +  /  (MnO2)  +  m  (NH^l)  -f  ;;  Zn. 
(After  sending  the  current) — 

kC+(l—  2)(Mn0.2)   +  (m  -  2)(NH4C1)  +  (Mn2O3)  +  2(NH3)   +   (H2O) 
+  (ZnCl2)  +  (»—  i)(Zn). 

The  letters  k,  I,  m,  n  represent  indefinite  amounts  of  the 
acting  substances. 

In  the  modified  Leclanche  cell  the  porous  cup  is  not 
needed,  as  compressed  prisms  of  manganese  dioxide,  gas 
carbon,  and  shellac  are  used  around  the  carbon  plate. 

The  Daniell  cell  (Fig.  4)  consists  of  a  glass  jar,  the 
porous  cup  T,  and  a  cylinder  of  zinc  (Z),  the  negative 
pole.  Outside  of  the  porous  cup  is  the  sheet-copper  cyl- 
inder K.  The  zinc  is  the  negative  electrode,  and  the  cop- 
per the  positive  electrode.  The  zinc  stands  in  dilute 
sulphuric  acid  (i  :  20),  and  the  copper  in  copper  sulphate. 
Zinc  sulphate  often  replaces  the  sulphuric  acid.  The 
chemical  action  in  the  cell  is  probably : — 


k  (Cu)  +  /  (CuSO4).  /Before  sending  \  .2  m  (ZnSO4)  +  n  (Zn). 

V      the  current     /  ~ 

I 

+  i)(Cu)  +  (/—  i)(CuS04).     /After  sending  §  (m  +  i)(ZnSO4)  -f  (n  —  i)(Zn). 
V  the  current.  /  g  (Ayrton.) 


c_ 


The  E.  M.  F.  of  this  cell  is  about  1.07.     The  Meidinger 
(Fig.  5)  and  Crowfoot  (Fig.  6)  cells  are  modifications  of  the 


SOURCES    OF   THE    ELECTRIC    CURRENT.  17 

Daniell,  and  very  serviceable  in  electrolytic  work  when 
currents  of  low  intensity  are  desired.     In  the  sketch  of  the 

FIG.  4. 


Meidinger  cell,  G  is  a  large  glass  jar ;  g,  a  small  glass  vessel, 
in  which  stands  the  copper  cylinder,  K  (  +  P).     Z  ( —  P) 


i8 


ELECTRO-CHEMICAL    ANALYSIS. 


is  a  cylinder  of  zinc.     B  contains  the  supply  of  copper 
sulphate  crystals. 

The  current  from  either  of  these  batteries  remains  quite 
constant  for  long  periods.  The  cells  themselves  do  not 
require  much  attention.  Half  a  dozen  of  either  of  these 
forms  will  do  nearly  all  the  electrolytic  work  of  an  ordinary 
laboratory.  The  "Crowfoot"  form  can  be  readily  and 


FIG.  7. 


cheaply  prepared.  Rejected 
the  neck  and  upper  portions, 
If  currents  of  greater  E.  M 
(Fig.  7)  or  Grove  cell  (Fig. 
former  there  is  zinc  in  dilute 
of  potassium  bichromate  and 
plate  in  a  cup  of  nitric  acid 


acid  bottles,  after  removing 
answer  well  as  jars. 
.  F.  are  required,  the  Bunsen 
8)  should  be  used.  In  the 
sulphuric  acid,  or  a  mixture 
sulphuric  acid,  and  a  carbon 
.  It  is  a  less  expensive  cell 


SOURCES    OF   THE    ELECTRIC    CURRENT.  1 9 

than  the  Grove,  as  platinum  is  not  employed.  It  is  not 
so  readily  handled,  and  consumes  more  nitric  acid.  Its 
electromotive  force  is  somewhat  less  than  that  of  the 
Grove  form.  In  the  latter  there  is  a  strip  of  platinum  (P) 
in  concentrated  nitric  acid  (in  the  porous  cup,  x),  and  zinc 
(22)  in  dilute  sulphuric  acid  (one  pint  of  acid  and  ten  pints 
of  water).  The  E.  M.  F.  is  1.93  volts.  When  acting, 
nitrogen  tetroxide  is  set  free;  this  can  be  in  a  measure 
suppressed  by  adding  ammonium  chloride  to  the  nitric 
acid.  The  chemical  changes  occurring  in  the  Bunsen  and 
Grove  cells  are  very  similar.  Ayrton  expresses  them  as 
follows  :— 

(Before  current  is  sent) — 

/fc(Pt)  +/(HNOa). 

OT  (H2S04)  +n(Zn). 
(After  sending  current) —  ~ 

*(Pt)  +  (/— 2)(HN03)  +  (No04)  +  (2H..O).    2     (»i  — i)(H2S04)  +  (ZnSO4)  + 

o  (n— i)(Zn). 

The  internal  resistance  of  the  Grove  cell  is  small.  To 
obtain  good  results  both  the  Bunsen  and  Grove  cells  re- 
quire constant  attention. 

In  amalgamating  the  zincs  in  any  of  the  preceding 
batteries,  first  allow  them  to  remain  over  night  in  very 
dilute  hydrochloric  acid,  then  immerse  in  mercury,  and 
with  a  wet  cloth  rub  the  latter  into  the  metal.  This 
should  be  done  once  a  week,  when  the  cells  are  in  daily 
use. 

The  Cupron  cell  (Fig.  9)  consists  of  two  amalga- 
mated zinc  plates,  between  which  is  suspended  a  porous 
copper  oxide  plate.  The  liquid  used  in  this  cell  is  an  18 
per  cent,  solution  of  commercial  caustic  soda.  The  E.  M. 
F.  is  0.85  volt.  The  liquid  should  cover  the  plates  com- 
pletely. In  case  of  prolonged  use  a  layer  of  paraffin  oil  is 


2O  ELECTRO-CHEMICAL    ANALYSIS. 

placed  on  the  surface  of  the  solution  to  exclude  the  carbon 
dioxide  of  the  air  as  much  as  possible.  This  form  of  bat- 
tery will  be  found  very  useful  for  general  electrolytic 
purposes. 

For  further  information  upon  batteries,  consult  Ayr- 
ton's  Practical  Electricity. 

Magneto-electric  machines  and  dynamos  have  been  used 
to  some  extent  in  electrolytic  decompositions,  but  a  de- 
tailed description  of  their  construction  will  not  be  given. 
It  will  be  sufficient  to  add  that  a  dynamo  with  a  tension 

FIG.  9. 


of  5  volts  will  answer  for  about  all  the  determinations, 
separations,  and  oxidations  which  are  carried  out  electro- 
lytically.  See  further  Smith's  OetteVs  Electrochemical 
Experiments,  pp.  27-37,  P.  Blakiston's  Son  &  Co., 
Philadelphia. 

Thermopiles  have  also  been  used  to  furnish  currents 
for  electrolytic  work.  Their  use  has  been  objected  to 
upon  the  ground  that  the  currents  afforded  by  them  are 
rarely  strong  enough  for  the  greater  number  of  determi- 
nations and  separations,  and  again  they  are  easily  broken 


SOURCES    OF   THE    ELECTRIC    CURRENT. 


21 


and  difficult  to  repair.     The  forms  generally  met  with  are 
those  recommended  by  Clamond  and  Noe. 

The  Clamond  thermopile  is  pictured  in  Fig.  10.  i  is  a 
perspective  view  of  the  same;  2  represents  a  vertical  sec- 
tion, and  3  a  basal  section,  showing  the  bars  and  arma- 
tures. The  elements  consist  of  bars  of  a  zinc  and  anti- 
mony alloy  and  a  strip  of  sheet-iron.  These  are  arranged 
in  circles,  as  indicated  in  3 ;  they  are  placed  one  above  the 

FIG.  10. 


other.  In  3,  B  represents  the  bars  of  zinc  and  antimony 
alloy,  while  the  tinned  sheet-iron  plates  are  marked  L. 
The  sheet-iron  serves  to  conduct  the  current  from  one 
element  to  the  other;  hence,  these  strips  rest  upon  the 
bars  B.  Heat  expands  the  latter,  and  in  consequence 
renders  the  contact  more  intimate.  The  single  elements, 
as  well  as  the  circles  of  elements,  are  separated  from  each 
other  by  plates  of  asbestos  (see  r  in  2 ) .  The  cylinder  itself 


ELECTRO-CHEMICAL    ANALYSIS. 

consists  of  a  series  of  such  circles.  The  welded  points  of 
the  bars  are  all  directed  to  the  centre  of  the  cylinder.  The 
gas  flames  are  prevented  from  coming  in  immediate  con- 
tact with  them  by  the  asbestos  lining  of  the  cylinder.  As 
gas  is  employed  to  furnish  the  necessary  heat,  in  the  mid- 
dle of  the  cylinder  will  be  observed  a  clay  tube  (A)  pro- 
vided with  apertures  (2  and  3).  The  gas  enters  through 
the  Giroud  regulator  C  (i  and  2),  which  makes  it  possible 
to  maintain  a  uniform  temperature  and  a  constant  cur- 
rent. From  C  it  is  conducted  to  A ,  through  T,  into  which 
air  is  admitted  by  suitable  apertures.  The  mixture  of  air 
and  gas  burns  at  the  openings  in  A.  Additional  air  is 
supplied  through  D.  Light  the  gas  jets  from  above,  after 
removing  the  cover.  The  poles  of  each  ring  of  elements 
end  in  binding  screws,  thus  enabling  the  operator  to  con- 
nect any  number  of  them,  depending  upon  the  external 
resistance  (Z.  f.  a.  Ch.,  15,  334).  When  in  excellent  con- 
dition, these  thermopiles  are  said  to  yield  a  current  equiv- 
alent to  400-500  c.c.  of  oxyhydrogen  gas  per  hour.  The 
form  of  thermopile  recently  devised  by  Gulcher  (Z.  f. 
ang.  Ch.  (1890),  Heft  18,  548;  Blectrotechnische  Zeit- 
schrift,  11,  187)  possesses  marked  advantages  over  the 
types  just  described.  It  is  decidedly  more  durable.  The 
largest  form  (Fig.  1 1 )  consumes  hourly  1 70  litres  of  gas  and 
develops  an  electromotive  force  of  4  volts,  with  an  internal 
resistance  of  0.6-0.7  ohm.  Those  who  have  used  this 
modified  thermopile  consider  it  extremely  valuable  in 
charging  storage  cells  for  use  in  electro-chemical  analysis. 

LITERATURE. — Z.  f.  a.  Ch.,  14,  350;    17,  205;  Ding.  p.  Jr.,  224,  267;  Z.  f. 
a    Ch.,  18,  457  ;  25,  539  ;   Z.  f.  ang.  Ch.  (1809),  Heft  18,  548. 

The  best  source  of  electric  energy,  for  electrolytic  pur- 


SOURCES   OF   THE    ELECTRIC    CURRENT.  23 

poses,  is  unquestionably  the  storage  cell  which  gives  a 
very  constant  current. 

A  form  of  this  cell  recently  developed  and  deserving 
mention  is  known  as  the  "Chloride  Accumulator"  (Fig. 
12);  it  is  of  the  Plante  type.  The  largely  increased  sur- 
face of  available  plate  for  corrosion  by  the  current  is  se- 
cured by  casting  a  frame  of  lead  around  square  or  circular 
tablets  of  lead  chloride  mixed  with  zinc  chloride,  and  then 

FIG.  ii. 


reducing  these  to  metallic  lead  by  means  of  zinc  in  an  acid 
zinc  chloride  solution.  In  this  way  a  plate  is  obtained 
which  is  readily  "formed"  by  the  action  of  the  current, 
the  oxygen  rapidly  converting  its  porous  portion  into  per- 
oxide. An  uneven  number  of  these  peroxidized  or  pos- 
itive plates  are  placed  with  an  even  number  of  the  metallic 
lead  or  negative  plates,  to  form  a  battery,  the  total  num- 
ber of  plates  being  fixed  by  the  capacity  required.  Thus, 
one  positive  plate  7!  inches  square,  placed  between  two 


24  ELECTRO-CHEMICAL    ANALYSIS. 

negative  plates  of  the  same  size,  and  immersed  in  sul- 
phuric acid  of  specific  gravity  1.275,  forms  a  battery  hav- 
ing a  normal  storage  capacity  of  50  ampere-hours.  The 
weight  of  the  plates  in  this  cell  is  13  pounds.  The  resis- 
tance of  the  "Chloride  Accumulator  "  is  very  low.  The 
great  merit  of  the  cell  lies  in  its  wide  adaptability  to  the 


FIG.  12. 


conditions  of  use.  It  can  be  charged  and  discharged  at 
varying  rates  without  injury,  and  shows  no  sulphating 
when  discharged  below  its  normal  minimum  voltage.  It 
is  manufactured  by  the  Electric  Storage  Co.,  of  Phila- 
delphia. 

Cells  of  this  kind  can  be  charged  from  primary  batteries, 


SOURCES    OF    THE    ELECTRIC    CURRENT.  25 

or,  better,  by  means  of  a  dynamo  or  thermopile  (p.  22). 
In  any  community  where  electric  lighting  is  employed  it 
is  possible  to  have  the  charging  done  at  little  expense,  and 
in  factories,  where  there  is  always  sufficient  power,  a  small 
dynamo  could  easily  be  arranged  for  this  purpose,  so  that 
almost  any  number  of  cells  could  be  kept  in  condition  for 
work.  The  iron  estimations  required  by  any  establishment 
could  be  rapidly  and  accurately  made  with  three  cells  of 
this  type;  little  attention  would  be  demanded  from  the 
chemist.  While  storage  cells  can  be  used  in  almost  every 
description  of  electrolysis,  there  are  a  great  many  cases 
where  economy  would  suggest  the  use  of  the  cheaper  bat- 
teries— e.  g.,  the  Crowfoot.  Consult  the  following  litera- 
ture upon  storage  batteries  :— 

Wied.  Ann.,  34  (1888),  583  ;  Proceedings  of  the  Royal  Society,  June  20,  1889  ; 
Transactions  of  Am.  Inst.  Mining  Engineers  (Electrical  Accumulators,  Salom), 
Feb. ,1890.  Elektrotechnische  Zeitschrift,  Jahrg.  1890;  Heppe,  Akkumulatoren 
fur  Elektrizitat,  Berlin,  1892;  Z.  f.  ang.  Ch.,  1892,  p.  451  ;  Ch.  Z.,  Jahrg.  17, 
66  ;  Die  Akkumulatoren,  Elbs,  2te  Auflage,  1896,  Leipzig  ;  Introduction  to  Elec- 
trochemical Experiments,  ¥.  Oettel  (translation  by  Smith),  Philadelphia, 
1897  ;  Pfitzner,  Die  elektrischen  Starkstrome,  Leipzig. 

Stillwell  and  Austen  have  recently  suggested  the  use  of 
the  electric  light  current  for  the  determination  of  metals 
in  the  electrolytic  way.  That  portion  of  their  communi- 
cation, in  which  is  embodied  all  that  is  essential  for  those 
desirous  of  adopting  this  method,  will  be  found  in  the 
following  quotation:  "The  whole  apparatus  can  be  made 
from  a  few  yards  of  insulated  copper  wire,  some  16  wooden 
lamp  sockets,  and  blackened  lamps,  say  six  5o-candle 
power,  three  32-candle  power,  six  24-candle  power,  and 
six  i6-candle  power Binding  screws,  con- 
nections, and  plugs  will  also  be  necessary  in  addition  to 
those  which  are  put  in  with  the  electric  wires. 
3 


26 


ELECTRO-CHEMICAL   ANALYSIS. 


''The  main  wires  +,  +  ,  — ,  are  furnished  with  sockets 
A,  B,  C  for  the  introduction  of  safety  plugs,  which,  for  the 


small  currents  used  in  electrolytic  work,  need  not  exceed 
6  lamp  leads.  The  main  wires  terminate  in  binding 
screws,  by  which  they  are  connected  with  the  series  of 


SOURCES   OF   THE    ELECTRIC    CURRENT.  27 

sockets  i,  2,  3,  4,  5.  In  these  lamps  for  reducing  the  main 
current  are  placed,  and  if  only  one  determination  or  like 
determinations  are  required  to  be  made,  only  this  series 
will  be  necessary  if  ordinary  currents  are  required.  If, 
however,  two  or  three  different  determinations,  or  some 
requiring  very  small  currents,  are  to  be  made,  side  cur- 
rents can  be  formed  as  around  sockets  2  and  4,  and  the 
current  brought  to  the  desired  size  by  the  introduction  of 
resistances  in  the  series  of  sockets  E  and  F.  K  and  L,  will 
represent  the  proper  position  of  the  solutions  to  be  elec- 
trolyzed  by  these  side  currents.  By  this  arrangement 
three  unlike  determinations  can  be  simultaneously  made, 
one  in  the  main  circuit,  and  one  in  each  of  the  side-series. 
If  more  determinations  are  required,  other  sets  of  sockets 
may  be  put  up  and  potentials  be  taken  over  other  lamps. 
The  sockets  may  be  placed  on  the  wall  above  the  desk,  the 
wires  leading  down  to  the  solutions  to  be  electrolyzed." 
(Jr.  An.  Ch.,  6,  129.)  Any  other  arrangement  can  be 
adopted.  That  just  described  can  be  adjusted  to  the 
parallel  system. 

The  current  may  be  derived  from  an  Edison  three- wire 
system  or  from  any  other  incandescent  system. 

Dr.  Hart,  of  Easton,  Pa.,  has  devised  a  resistance  frame 
to  be  used  when  the  electric  light  current  is  employed  for 
electrolytic  purposes.  It  is  simpler  in  construction  than 
that  described  in  the  preceding  paragraph.  Baker  & 
Adamson,  of  Easton,  manufacture  this  frame;  particulars 
in  regard  to  it  can  be  obtained  from  them. 

Having  thus  briefly  described  the  more  important  cur- 
rent-producers, the  means  of  regulating  the  current  may 
be  next  considered. 


28 


ELECTRO-CHEMICAL    ANALYSIS. 


4.  REDUCTION  OF  THE  CURRENT. 

It  is  often  necessary  to  reduce  strong  currents.  Per- 
sons acquainted  with  practical  physics  will  promptly  sug- 
gest the  resistance  coils  found  in  physical  laboratories  as 
vSuitable  for  this  purpose.  They  are,  on  the  whole,  quite 
satisfactory,  and  have  been  thus  utilized,  although  simpler 
and  more  convenient  current-reducers  have  made  their 


FIG.  14. 


appearance  in  recent  years.     A  few  of  these  later  appli- 
ances may  be  mentioned : — 

The  current  may  be  sent  through  a  solution  (satu- 
rated) of  zinc  sulphate,  contained  in  a  large  glass  cylinder, 
about  22  cm.  long  and  8.5  cm.  in  diameter.  In  one  ex- 
periment the  current  is  passed  from  a  to  b  (Fig.  14),  and 
in  the  next  from  b  to  a.  "  The  rod  b,  with  one  zinc  pole, 
is  pushed  toward  the  zinc  pole  a,  until  the  current  reaches 
the  desired  strength."  It  is  well  to  amalgamate  the  zincs 


REDUCTION  OF  THE  CURRENT. 


29 


from  time  to  time.  We  are  indebted  for  this  piece  of 
apparatus  to  Classen,  who  has  also  described  another 
simple  rheostat  (Fig.  15)  (Ber.,  21,  359).  In  this  appa- 
ratus the  current  enters  at  a,  travels  the  German  silver 
resistance  N,  and  returns  through  b  to  the  battery.  In  the 
performance  of  electrolytic  depositions  the  platinum  ves- 
sels, serving  as  negative  electrodes,  may  be  connected 

FIG.  15. 


with  any  one  of  the  binding-posts  from  i  to  20.  This 
makes  it  possible  for  the  analyst  to  execute  eight  different 
determinations  at  the  same  time.  To  show  the  influence 
of  this  apparatus,  a  current  from  five  Bunsen  cells,  gener- 
ating 68  c.c.  of  oxyhydrogen  gas  per  minute,  was  allowed 
to  act  upon  copper  solutions  contained  in  six  vessels.  The 
current  at  binding-post  i  was  found  to  be  equal  to  3.75 
amperes;  at  2,  it  equaled  2.617  amperes;  at  3,  2.085 
amperes;  at  4,  1.911  amperes,  etc.,  until  at  20  it  was  only 
0.098  of  an  ampere. 


3O  ELECTRO-CHEMICAL    ANALYSIS. 

To  better  understand  these  figures  it  should  be  remem- 
bered that  an  ampere  equals  10.436  c.c.  of  oxyhydrogen 
gas  per  minute,  or  it  is  equivalent  to  a  current  which  will 
precipitate  19.69  mg.  of  metallic  copper,  or  67.1  mg.  of 
metallic  silver  in  one  minute. 

For  a  larger  form  of  apparatus  somewhat  similar  to  that 


FIG.   17. 


FIG.  i 6. 


described  above,  see  Ber.,  17,  1787.     Figs.  16  and  17  rep- 
resent other  forms  of  convenient  and  helpful  rheostats. 

The  writer  has  for  some  time  employed  a  much  simpler 
current-reducer,  which  has  the  advantage  of  cheapness 
and  ready  construction  to  recommend  it.  It  consists  of  a 
light  wooden  parallelogram,  about  six  feet  in  length. 
Extending  from  end  to  end,  on  both  sides,  is  a  light  iron 
wire,  measuring  in  all  about  500  feet  (Fig.  18).  With  the 


REDUCTION  OF  THE  CURRENT.  31 

binding-posts  at  a  and  6,  and  a  simple  clamp,  it  is  possible 
to  throw  in  almost  any  resistance  that  may  be  required. 


FIG.   18. 


It  answers  all  practical  purposes.     It  can  be  procured 
from  Queen  &  Co.,  Philadelphia,  Pa. 

LITERATURE. — v.  Klobuko  w,  Jr.  f.  pkt.  Ch.,  37,  375  ;  40,121;  Oettel's 
Electrochemical  Experiments  (Smith),  P.  Blakiston's  Son  &  Co.,  Phila. 


ELECTRO-CHEMICAL    ANALYSIS. 


5.   MEASURING    CURRENTS,    VOLTAMETER, 

AMPEREMETER. 

In  every  analysis  by  electrolysis  it  is  advisable  that  the 
strength  of  the  acting  current  should  be  known.     The 

FIG.  19. 


Bunsen  voltameter  (Fig.  19)  may  be  used  for  this  purposes 
The  inner  tube  a,  containing  sulphuric  acid  of  sp.  gr.  1.22, 
stands  in  a  large  cylinder  of  water  to  cool  it.  The  liber- 


MEASURING    CURRENTS.  33 

ated  hydrogen  and  oxygen  are  collected  over  water  in  the 
eudiometer  tube  R ;  p  and  p'  are  platinum  electrodes.  In 
all  accurate  experiments  the  volume  of  gas  should  always 
be  reduced  to  o°  and  760  mm.  pressure.  Voltameters  of 
this  description  are  only  in  rare  cases  adapted  for  current 
measurement  by  introduction  into  the  circuit.  To  read 
them  the  current  must  generally  be  interrupted,  and  they 
augment  the  resistance  of  the  circuit  to  a  marked  degree, 
hence  many  chemists  substitute  a  galvanometer  (tangent 
or  sine)  for  the  voltameter.  The  deflection  of  the  needle 
by  the  current  measures  the  strength  of  the  latter.  "  In 
order  to  express  in  terms  of  chemical  action  the  deflection 
of  the  needle,  it  is  placed  in  the  same  current  with  a 
voltameter,  and  the  deviation  of  the  needle  is  observed, 
as  well  as  the  volume  of  electrolytic  gas  (reduced  to  o°  and 
760  mm.  pressure)  which  is  produced  in  a  minute.  Plac- 
ing the  volume  equal  to  v,  the  quotient  ^-^  gives  the 
standard  value  for  the  galvanometer.  If  this  standard 
value  is  denoted  by  R,  the  strength,  I,  of  a  current  which 
produces  the  deviation  a  is  I  =  R  tan.  a." 

The  writer  has  found  the  amperemeter  of  Kohlrausch 
(Fig.  20)  very  satisfactory,  especially  in  cases  where  strong 
currents  are  employed.  In  this  instrument  the  current 
travels  through  an  insulated  wire  surrounding  a  bar  of  soft 
iron.  The  latter,  in  its  magnetized  state,  attracts  a  needle 
or  indicator  and  causes  it  to  move  over  a  vertical,  gradu- 
ated scale  (in  amperes),  and  its  deflection  gives  at  once  the 
strength  of  the  current  in  amperes.  The  Weston  milli- 
amperemeters  and  ammeters  will  also  prove  most  valua- 
ble in  this  connection. 

In  electrolytic  work  of  any  kind  it  is  advisable  that  the 
apparatus  intended  to  measure  the  current  strength 
should  be  in  the  circuit  during  the  entire  decomposition, 

4 


34 


ELECTRO-CHEMICAL    ANALYSIS. 


for  it  is  only  in  this  way  that  we  can  expect  to  effect  sepa- 
rations without  encountering  unpleasant  difficulties.  It 
is  necessary  to  know  just  what  energy  is  required,  and 
then  to  so  regulate  the  current  that  the  same  is  approxi- 
mately maintained  throughout  the  entire  determination. 


When  metals  were  first  determined  electrolytically  no 
attention  was  given  to  certain  very  important  factors. 
"Strong"  and  "feeble"  currents,  or  currents  from  a  two- 
cell  bichromate  battery,  or  five  large  Bunsen  cells,  etc., 
were  indicated.  Measuring  instruments  were  not  often 
used.  Rarely  was  anything  said  of  the  size  of  the  cathode 


MEASURING   CURRENTS.  35 

upon  which  the  metal  was  deposited,  or  of  the  forms  of 
the  anode,  the  degree  of  dilution  of  the  solution,  and  sim- 
ilar facts.  Confusion  naturally  arose  and  contradictory 
statements  of  one  kind  and  another  were  numerous. 
But  in  this,  as  in  all  other  questions  where  there  was  a 
real  desire  to  arrive  at  the  truth,  honest  experiment 
soon  pointed  the  way  in  which  changes  were  necessary 
and  also  demonstrated  the  conditions  to  be  observed  in 
order  that  satisfactory  results  might  be  obtained.  Prob- 
ably then,  as  at  present,  the  metal  depositions  were 
mainly  made  in  platinum  dishes,  or  upon  cylinders  or 
cones.  These  receptacles,  as  well  as  the  various  anode 
forms,  will  receive  thorough  consideration  later.  It  is 
the  purpose  of  the  writer  at  this  point  to  merely  empha- 
size the  most  essential  features  in  an  electrolytic  deter- 
mination or  separation.  Hence  note: — 

1.  The  current  density.     To  this  end  the  inner  surface 
of  the  platinum  dish  in  which  the  electrolysis  is  made 
should  be  known  in  cm2 ;  its  contents,  too,  should  be  given 
in  cm3  for  various  heights.     N.D100  is  the  normal  density  of 
the  current ;  this  is  equivalent  to  the  current  strength  for 
TOO  cm2  of  the  electrode  surface.     The  density  (D)  there- 
fore is  dependent  upon  the  current  strength,  as  well  as 
upon  the  surface  (E)  of  the  electrode  upon  which  the 
metallic  deposit  is  precipitated,  i.  e.,  D  =  ~. 

When  the  surface  upon  which  the  metal  is  deposited 
equals  E,  the  corresponding  current  strength  can  be  de- 
duced from  the  formula  C  ==  (N.D100).-^.  See,  further, 

Miller  and  Kiliani,  Lehrbuch  der  analyt.  Chemie,  4th  ed., 
pp.  17-24. 

2.  The  potential  across  the  poles, — the  pole  pressure, — 
which  is  best  determined  by  means  of  a  Weston  voltmeter 
(P-  59)-     This  is  a  very  important  factor.     A  number  of 


30  ELECTRO-CHEMICAL   ANALYSIS. 

interesting  separations  have  been  made  by  carefully  regu- 
lating the  pressure — voltage.     See  Z.  f .  ph.  Ch.,  12,  97. 

3.  The  form  of  the  anode — whether  a  flat  spiral,  a  disc 
of  platinum,  or  a  smaller  perforated  dish,  suspended  in  the 
electrolyte — should  also  be  observed,  as  well  as  its  distance 
from  the  cathode. 

4.  The  total  dilution  of  the  electrolyte  and  its  tempera- 
ture are  items  of  value. 

5.  The   ammeter   and  voltmeter  should  always  be   in 
the  circuit. 

Under  the  individual  metals  these  points  will  be  taken 
up  more  fully.  By  strict  adherence,  however,  to  these 
cardinal  features  no  one  need  fear  the  outcome.  It  will 
in  every  way  be  satisfactory. 

As  the  importance  of  electro-chemical  analysis  has 
become  evident,  there  has  been  marked  improvement  in 
the  various  forms  of  apparatus  used  in  this  work,  and  in- 
creased facilities  for  the  same  are  noticed  on  all  sides.  In 
every  well-appointed  laboratory  provision  is  made  for  this 
field  of  study,  and  in  certain  institutions  rooms  are  set 
aside  and  especially  equipped  to  carry  out  such  work. 
Here  at  the  University  of  Pennsylvania,  where  electro- 
lytic determinations  were  made  as  early  as  1878,  with  no 
special  appointments  and  with  the  most  primitive  forms 
of  apparatus,  there  has  been  a  gradual  evolution  and  de- 
velopment in  apparatus  and  facilities  according  to  de- 
mands and  with  increased  knowledge,  until  recently  an 
installation  has  been  made  for  this  as  well  as  for  other 
lines  of  work  in  electro-chemistry,  which  is  characterized 
by  great  completeness  and  such  simplicity  that  a  brief 
sketch  of  the  plant  may  be  well  introduced  here. 


AN  ELECTRO-CHEMICAL  LABORATORY.  37 

AN  ELECTRO-CHEMICAL  LABORATORY. 

This  laboratory  will  accommodate  at  least  sixteen  stu- 
dents, working  continuously.  The  room  available  for 
this  purpose  (Fig.  21)  is  fifteen  feet  by  twenty-six  feet, 
thus  affording  each  individual  three  feet  by  twenty  inches 
of  table  space. 

FIG.   21. 


ELECTRO-CHEMICAL  LABORATORY. 


Storage  cells  supply  the  energy.  Those  in  use  have  a 
capacity  of  1 20  ampere-hours,  with  a  normal  discharge  rate 
of  15  amperes  and  a  maximum  rate  of  30  amperes.  The 
compartments,  indicated  at  the  end  of  the  room,  contain 
two  groups  of  twenty -four  cells  each.  They  supply  their 
respective  sides  of  the  room.  They  are  supported  on 
racks  of  four  shelves  each,  six  cells  per  shelf.  Each  shelf 
is  thoroughly  paraffined  and  a  half -inch  layer  of  ground 


30  ELECTRO-CHEMICAL   ANALYSIS. 

quartz  is  placed  around  the  jars.  Fig.  22  shows  one  of 
these  compartments  with  the  lead  wires  and  cut-outs  for 
each  cell. 

The  switchboards  are  three  in  number,  two  of  them  each 

FIG.  22. 


BATTERY  ROOM. 


controlling  the  six  places  on  their  respective  sides  of  the 
room,  and  the  third  controlling  the  four  places  in  the  cen- 
tre. The  face  of  one  of  these  boards  is  shown  in  Fig.  23, 
the  letters  on  the  face  referring  to  the  working  tables  con- 
trolled. 

The  switchboard  on  the  east  side  of  the  room  consists  of 


AN  ELECTRO-CHEMICAL  LABORATORY. 


39 


a  slab  of  enameled  slate  twenty-four  by  thirty-four  inches, 
one  inch  thick,  and  contains,  for  each  of  the  six  outlets  to 

FIG.  23. 


DISTRIBUTING  BOARD. 


be  controlled,  one  circle  of  twenty-five  contact  pieces,  and 
has  two  spring  levers,  insulated  from  each  other  and  mov- 


4O  ELECTRO-CHEMICAL    ANALYSIS. 

ing  about  a  common  centre,  sweeping  over  them.  The 
contact  blocks  are  numbered  consecutively  from  o  to  24 
and  a  stop  is  provided  to  prevent  the  levers  from  sweeping 
past  the  zero.  Cell  No.  i  is  connected  between  blocks 
numbered  o  and  i  in  each  of  the  six  circles,  cell  No.  2  be- 
tween blocks  numbered  i  and  2,  and  so  on  for  the  re- 
mainder of  the  twenty-four  cells  in  that  group,  so  that  all 
blocks  similarly  numbered  on  the  one  board  are  connected 
together,  and  but  a  single  wire  leads  from  the  six  similarly 
numbered  blocks  to  the  junction  between  two  cells.  In 
this  lead  is  provided  the  usual  fuse.  The  circles  are  let- 
tered A,  B,  C,  etc.,  consecutively,  corresponding  with  the 
letters  at  the  outlets  to  be  controlled. 

Should  the  operator  at  the  outlet  E,  for  instance,  need 
two  cells,  he  goes  to  this  board,  and  finding  that  the  cells 
from  the  twelfth  cell  forward  are  not  being  used  in  any  of 
the  circles,  he  places  one  of  the  levers  on  contact  block  No. 
12  and  the  other  one  on  No.  14.  There  is  thus  very  little 
chance  of  doing  anything  wrong,  or  for  persons  to  inter- 
fere with  one  another,  because  there  is  no  necessity  to  use 
the  same  cells,  and  at  a  glance  one  can  observe  which  cells 
are  in  use.  Fig.  24  shows  the  electrical  connections  from 
one  of  these  distributing  boards  to  the  cells  and  outlets  on 
the  working  tables.  The  levers  themselves  are  too  narrow 
at  their  outer  ends  to  reach  across  from  one  block  to  an- 
other, to  prevent  short-circuiting  the  cells,  so  they  are 
provided  with  fibre  extensions  on  each  side  to  prevent 
their  falling  between  the  blocks,  and  also  to  prevent  their 
making  contact  with  each  other. 

The  switchboard  on  the  west  wall  is  exactly  similar  to 
the  one  just  described.  It  contains  the  circles  G,  H,  I, 
K,  L/,  and  M,  while  the  third  one,  which  controls  the  four 
outlets  on  the  centre  table,  is  only  twenty-four  inches 


AN    ELECTRO-CHEMICAL    LABORATORY.  41 

square,  but  has  twenty-six  contact  blocks  in  each  circle. 
They  are  numbered  o,  24,  25,  26,  and  so  on  to  48.  Be- 
tween the  two  blocks  numbered  o  and  24  are  connected  the 
cells  of  the  group  on  the  east  side  of  the  room;  between 
the  blocks  24  and  25  is  connected  cell  No.  i  of  the  west 
side  of  the  room,  while  cell  No.  2  is  connected  between 
blocks  numbered  25  and  26.  This  arrangement  connects 
the  two  groups  of  cells  in  series,  and  permits  the  use  of 
from  one  to  forty-eight  cells  at  the  centre  table  when 

FIG.  24. 


CONNECTIONS  TO  WORKING  TABLE. 

necessity  requires.  It  will,  perhaps,  have  been  noticed 
that  there  is  no  provision  made  for  connecting  cells  in 
parallel,  and  this  is  not  necessary,  as  the  maximum  dis- 
charge rate  of  the  cells  exceeds  the  greatest  estimated 
current  needed  by  one  operator. 

All  brass  parts  on  the  back  of  the  board,  as  well  as  the 
bared  ends  of  the  wires,  are  thoroughly  coated  with  P. 
and  B.  paint,  while  the  brass  parts  on  the  front  are  heavily 
lacquered  to  prevent  corrosion.  The  surface  of  the  con- 
tact blocks  can  easily  be  cleaned  with  fine  sandpaper. 


42  ELECTRO-CHEMICAL    ANALYSIS. 

The  measuring  instruments,  after  some  deliberation, 
were  chosen  of  the  switchboard  type.  While  this  neces- 
sitated procuring  at  least  one-third  more  instruments,  yet 
the  initial  cost  was  considerably  lower  than  if  portable 
instruments  had  been  provided,  and  experience  with 
portable  instruments  has  shown  that  a  greater  accuracy 
will  be  attained  with  switchboard  instruments  of  a  good 
form,  if  not  immediately,  yet  surely  after  the  first  six 
months  of  use. 

Each  outlet  is  provided  with  a  fused  switch,  a  volt- 
meter, two  ammeters,  a  rheostat,  and  a  terminal  board. 
They  are  connected  as  shown  in  Fig.  24.  The  positive 
lead  after  passing  through  the  variable  resistance  runs 
directly  to  the  positive  binding-post.  The  wire  coming 
from  the  negative  binding-post  runs  to  the  low-reading 
ammeter  and  thence  to  the  negative  side  of  the  switch, 
while  the  negative  post  marked  25  is  connected  to  the 
same  switch  terminal,  but  through  the  ammeter  of  large 
capacity.  The  anode  of  the  electrolytic  cell  is  therefore 
always  connected  to  the  middle  binding-post  and  the 
cathode  either  to  post  i  or  25,  depending  upon  the 
strength  of  current  it  is  intended  to  pass  through  the  cell. 
The  voltmeter,  being  connected  as  shown,  measures  the 
potential  differences  at  the  terminals  of  the  cell,  except 
for  the  addition  of  the  small  fall  of  potential  through  the 
ammeters. 

The  voltmeters  on  the  side  of  the  room  have  scales 
ranging  from  o  to  50,  and  divided  to  1-2  volts.  Those  on 
the  centre  table  range  from  o  to  1 20. 

The  ammeters  ranging  from  o  to  i  ampere  are  divided 
to  i-ioo,  and  those  reading  from  o  to  25  are  divided  to  1-5 
amperes.  The  three  instruments  are  mounted  side  by 
side  on  an  oak  backboard  extending  the  whole  length  of 


AN  ELECTRO-CHEMICAL  LABORATORY.        43 

the  room  and  are  covered  by  an  air-tight  case  with  a  glass 
front,  as  shown  in  Fig.  25.  The  cases  have  neither  doors 
nor  a  back,  but  are  simply  screwed  against  a  backboard 
with  a  heavy  felt  gasket,  making  the  joint.  The  wires 

FIG.  25. 


WORKING  TABLE. 

come  out  through  hard  rubber  tubes  sealed  at  their  outer 
ends  by  insulating  tape. 

The  rheostats  are  of  the  enameled  type,  chosen  because 
of  their  being  impervious  to  fumes.  They  have  a  total 
resistance  of  172  ohms,  divided  into  51  steps  in  such  a 
way  that  their  resistances  form  a  geometrical  progression, 
the  first  step,  and  the  sum  of  all  the  steps,  being  chosen  in 


44  ELECTRO-CHEMICAL    ANALYSIS. 

accordance  with  data  of  the  resistances  of  the  baths  deter- 
mined for  the  work  done  under  an  earlier  system. 

The  wires,  both  those  in  the  battery  rooms  and  those  in 
the  laboratory  proper,  are  covered  with  rubber,  and  those 
in  the  laboratory  are  further  encased  in  oak  moulding,  but 
this  rather  for  the  sake  of  appearance  than  for  protection. 
The  whole  installation,  as  well  as  the  other  fittings  of  the 
room,  has  a  very  neat  and  finished  appearance.  (Science, 
13,  697  (1901).) 

Before  taking  up  the  description  of  the  details  to  be 
observed  in'  the  electrolytic  precipitation  of  individual 
metals,  it  may  not  be  uninteresting  to  briefly  trace  the 
history  of  the  introduction  of  the  electric  current  into 
chemical  analysis. 


6.   HISTORICAL. 

Although  the  early  years  of  last  century  show  consid- 
erable activity  in  electrical  studies,  the  efforts  were  mainly 
directed  to  the  solution  of  the  physical  side  of  electrolysis. 
To  Gaultier  de  Claubry  probably  belongs  the  credit  of 
having  first  (1850)  applied  the  current  to  the  detection  of 
metals  when  in  solution.  His  efforts  were  wholly  directed 
to  the  isolation  of  metals  from  poisons  by  depositing  the 
same  upon  plates  of  platinum.  When  the  precipitation 
was  considered  finished  the  plates  were  removed,  carefully 
washed,  and  the  deposited  metals  brought  into  solution 
with  nitric  acid,  and  there  tested  for  and  identified  by  the 
usual  course  of  analysis.  The  current  was  evidently  very 
feeble,  as  the  time  recorded  as  necessary  for  the  deposition 
varied  from  ten  to  twelve  hours.  Gaultier  considered  this 
method  reliable  in  all  instances,  but  especially  recom- 


HISTORICAL.  45 

mends  it  for  the  separation  of  copper  from  bread.  In 
testing  for  zinc  he  employed  a  strip  of  tin  as  anode,  but 
states  that  a  platinum  plate  will  answer  as  well. 

In  Graham-Otto's  Lehrbuch  der  Chemie  (1857)  it  is 
stated  that  the  oxygen  developed  at  the  positive  electrode 
readily  induces  the  formation  of  peroxides ;  .  .  .  that 
lead  and  manganese  peroxides  are  deposited,  from  solu- 
tions of  these  metals,  upon  the  positive  electrode  of  the 
battery;  .  .  .  that  the  point  of  a  platinum  wire, 
when  attached  to  the  anode  of  a  cell,  is  therefore  a  delicate 
means  of  testing  for  manganese  and  lead.  In  the  same 
text  the  oxidizing  power  of  the  anode  is  nicely  shown  by 
the  following  simple  experiment :  A  piece  of  iron,  in  con- 
nection with  the  positive  electrode  of  the  battery,  is  intro- 
duced into  a  V-shaped  glass  tube  containing  a  concen- 
trated solution  of  potassium  hydroxide,  while  a  platinum 
wire  running  from  a  negative  electrode  projects  into  the 
other  limb  of  the  vessel.  In  a  short  time  ferric  acid  ap- 
pears around  the  anode,  and  is  recognized  by  its  color. 

C.  Despretz  (1857)  described  the  decomposition  of  cer- 
tain salts  by  means  of  the  electric  current,  and  remarked 
that,  while  operating  with  solutions  of  the  acetates  of 
copper  and  lead,  he  expected  both  metals  would  be  de- 
posited upon  the  negative  pole,  and  was  much  surprised 
to  find  that  the  lead  separated  as  oxide  upon  the  anode  at 
the  same  time  that  the  copper  was  deposited  upon  the 
cathode.  The  results  were  the  same  when  experiments 
were  conducted  with  the  nitrates  and  pure  acetates. 
With  manganese  no  deposition  took  place  upon  the  nega- 
tive electrode,  but  a  black  oxide  appeared  at  the  opposite 
pole.  Potassium  antimonyl  tartrate  gave  a  crystalline 
metallic  deposit  of  antimony  at  the  cathode,  and  upon  the 
anode  a  yellowish-red  coating,  supposed  to  be  anhydrous 


46  ELECTRO-CHEMICAL    ANALYSIS. 

antimonic  acid.  Bismuth  nitrate  yielded  a  reddish- 
brown  deposit  at  the  positive  electrode.  Despretz  con- 
cludes his  paper  by  stating  that  although  the  facts  were 
few  in  number,  yet  they  were  new  in  so  far  as  they  con- 
cerned lead,  antimony,  and  manganese;  and,  furthermore, 
that  the  separation  of  copper  from  lead  by  the  current  was 
almost  perfectly  complete. 

Three  years  later  (1860)  Charles  L/.  Bloxam  recom- 
mended the  process  of  Gaultier  for  the  detection  of  metals 
in  organic  mixtures,  although  it  may  not  be  improper  to 
add  that  Smee  (1851),  in  his  work  on  electrometallurgy, 
asserts  that  Morton  was  the  first  person  to  employ  the 
electric  current  for  the  isolation  of  metals  from  poisonous 
mixtures.  However  this  may  be,  the  fact  remains  that 
Bloxam  did  use  the  current  quite  extensively  for  this  pur- 
pose, and  while  he  claims  no  quantitative  results  for  the 
method,  the  apparatus  employed  by  him  and  his  subse- 
quent work  in  this  direction  deserve  great  credit. 

To  detect  arsenic  electrolytically  Bloxam  made  use  of  a 
glass  jar,  four  cubic  inches  in  capacity,  closed  below  by 
parchment,  which  was  tightly  secured  by  means  of  a  thin 
platinum  wire.  In  the  neck  of  the  jar  was  a  large  cork, 
through  which  passed  a  glass  tube  bent  at  a  right  angle. 
This  tube  was  intended  to  serve  as  a  means  of  escape  for 
the  gases  liberated  within  the  jar.  The  platinum  wire 
from  the  negative  electrode  was  also  held  in  position  by 
the  cork.  The  portion  of  the  wire  within  the  jar  was 
attached  to  a  platinum  plate  dipping  into  the  arsenical 
mixture  containing  dilute  sulphuric  acid.  The  jar  with 
its  contents  stood  in  a  wide  beaker,  filled  with  water,  into 
which  dipped  the  positive  electrode  of  the  battery. 
Under  the  influence  of  the  current,  metals  like  antimony, 
copper,  mercury,  and  bismuth  separated  upon  the  plati- 


HISTORICAL.  47 

num  plate  of  the  negative  electrode,  while  arsine  was 
liberated  and  escaped  through  the  exit-tube  into  some 
suitable  absorbing  liquid.  To  ascertain  what  metal  or 
metals  had  separated  upon  the  cathode,  the  plate  attached 
thereto  was  removed,  after  the  interruption  of  the  cur- 
rent, and  treated  with  hot  ammonium  sulphide.  Upon 
evaporating  this  solution  an  orange-colored  spot  remained 
if  antimony  had  been  previously  present.  If  a  metallic 
deposit  continued  to  adhere  to  the  foil,  the  latter  was 
acted  upon  by  nitric  acid  to  effect  the  solution  of  the  re- 
maining metals. 

J.  Nickles  (1862)  precipitated  silver  with  the  current 
obtained  from  a  zinc-copper  couple.  The  positive  elec- 
trode consisted  of  a  piece  of  graphite,  taken  from  a  lead- 
pencil,  while  a  thin,  bright  copper  wire  constituted  the 
negative  electrode.  The  silver  separated  upon  this.  The 
current  was  very  feeble,  for  hydrogen  was  not  liberated  at 
the  cathode.  Nickles  also  suggested  the  reduction  of 
large  quantities  of  silver  from  the  solution  of  its  cyanide 
by  this  means.  To  obtain  the  silver  he  advised  using  a 
cylindrical  cathode  constructed  from  some  readily  fusible 
alloy,  so  that  after  the  reduction  was  finished  the  other 
metals  might  be  easily  melted  out  and  leave  a  silver  plate. 
Copper,  lead,  bismuth,  and  antimony  were  separated 
electrolytically,  by  Nickles,  from  textiles. 

In  1862  A.  C.  and  E.  Becquerel  resumed  their  electro- 
chemical investigations,  first  begun  some  thirty  years 
previously.  Their  experiments  seem  to  have  been  aimed 
chiefly  toward  the  reduction  of  metallic  solutions  upon  a 
large  scale,  caring  not  for  the  quantitative  estimation  of 
metals,  but  seeking  rather  a  rapid  and  satisfactory  tech- 
nical isolation  process. 

Wohler  (1868)  found  that  when  palladium  was  made 


48  ELECTRO-CHEMICAL    ANALYSIS. 

the  positive  conductor  of  two  Bunsen  cells,  and  placed  in 
water  acidulated  with  sulphuric  acid,  it  immediately  be- 
came covered  with  alternating,  bright,  steel-like  colors. 
He  regarded  the  coating  as  palladium  dioxide,  since  it 
liberated  chlorine  when  treated  with  hydrochloric  acid, 
and  carbon  dioxide  when  warmed  with  oxalic  acid. 
Black  amorphous  metal  separated  at  the  cathode.  Its 
quantity  was  slight.  Under  similar  conditions  lead  also 
yields  the  brown  dioxide,  and  the  same  may  be  said  of 
thallium.  Osmium,  in  its  ordinary  porous  form,  at  once 
becomes  osmic  acid.  When  caustic  alkali  is  substituted 
for  the  acid,  the  liquid  rapidly  assumes  a  deep  yellow 
color,  while  a  thin  deposit  of  metal  appears  upon  the 
cathode.  Ruthenium  behaves  similarly  when  applied  in 
the  form  of  powder.  Osmium-iridium,  a  compound  de- 
composed with  difficulty  under  ordinary  circumstances, 
immediately  passes  into  solution  when  brought  in  contact 
with  the  positive  electrode  of  a  battery  placed  in  a  solution 
of  sodium  hydroxide,  and  imparts  a  yellow  color  to  the 
alkaline  liquid.  A  black  deposit  of  metal  slowly  makes  its 
appearance  upon  the  negative  pole. 

The  experiments  thus  far  described  are  qualitative  in 
their  results.  The  first  notice  of  the  quantitative  estima- 
tion of  metals  electrolytically  was  that  of  Wolcott  Gibbs 
(1864),  when  he  published  the  results  he  had  obtained 
with  copper  and  nickel.  I/uckow,  in  alluding  to  this  work 
a  year  later  (1865),  says:  "I  take  the  liberty  to  observe 
that  so  far  as  the  determination  of  copper  is  concerned,  I 
estimated  that  metal  in  this  manner  more  than  twenty 
years  ago,  and  as  early  as  1860  employed  the  electric 
current  for  the  deposition  of  copper  quantitatively  in 
various  analyses."  It  was  L/uckow  who  proposed  the 
name  Elektro-Metall  Analyse  for  this  new  method  of 


HISTORICAL.  49 

quantitative  analysis.     According  to  this  writer  the  cur- 
rent may  be  applied  as  follows  :— 

1 .  To  dissolve  metals  and  alloys  in  acids  by  which  they 
would  not  be  affected  unaided  by  the  electric  current. 

2.  To  detect  metals  like  manganese  and  lead  (silver, 
nickel,  cobalt) ;  separating  them  in  the  form  of  peroxides ; 
also  manganese  as  permanganic  acid. 

3.  To  separate  various  metals,  e.  g.,  copper  and  man- 
ganese, from  zinc,  iron,  cobalt,  and  nickel. 

4.  To  deposit  and  estimate  metals  quantitatively,  in 
acid,  alkaline,  and  neutral  solutions. 

5.  For  various  reductions,  e.  g.,  silver  chloride,  basic 
bismuth  chloride,  and  lead  sulphate,  in  order  that  the 
metals  in  them  may  be  determined.     To  reduce  chromic 
acid  to  oxide,  e.  g.,  potassium  bichromate  acidulated  with 
dilute  sulphuric  acid. 

These  applications  embrace  nearly  all  that  has  since 
been  accomplished  by  the  aid  of  the  current.  In  the  same 
article  to  which  I/uckow  calls  attention  to  the  facts  re- 
corded above,  he  describes  minutely  the  method  pursued 
by  him  in  the  precipitation  of  metals.  Reference  to  these 
early  experiments  will  show  with  what  care  and  accuracy 
every  detail  was  worked  out.  Luckow  also  announced 
"that  all  the  lead  contained  in  solution  was  deposited  as 
peroxide  upon  the  positive  electrode,  and  might  be  deter- 
mined from  the  increased  weight  of  the  latter."  This 
observation  was  fully  confirmed  by  Hampe,  and  later  by 
W.  C.  May. 

Wrightson  (1876)  called  attention  to  the  fact  that  if 
solutions  of  copper  were  electrolyzed  in  the  presence  of 
other  metals,  the  latter  greatly  influenced  the  separation 
of  the  former.  For  example,  with  copper  and  antimony, 
the  deposition  of  the  copper  was  always  incomplete  when 
5 


5O  ELECTRO-CHEMICAL    ANALYSIS. 

the  antimony  equaled  one-fourth  to  two-thirds  the  quan- 
tity of  the  former.  Notwithstanding,  a  complete  separa- 
tion of  the  two  metals  can  be  effected  when  the  quantity 
of  the  antimony  is  small.  A  somewhat  similar  behavior 
was  noticed  with  other  metals.  The  deposition  of  cad- 
mium, zinc,  cobalt,  and  nickel  was  apparently  not  satis- 
factory. 

L/ecoq  de  Boisbaudran  (1877)  electrolyzed  the  potas- 
sium hydroxide  solution  of  the  metal  gallium,  using  six 
Bunsen  elements  with  20-30  c.c.  of  the  concentrated 
liquid.  The  deposited  metal  was  readily  detached  when 
the  negative  electrode  was  immersed  in  cold  water  and 
bent  slightly. 

The  unpromising  behavior  of  zinc  solutions,  observed 
by  Wrightson,  was  fortunately  overcome  by  Parodi  and 
Mascazzini  (1877),  wno  employed  a  solution  of  the  sul- 
phate, to  which  was  added  an  excess  of  ammonium 
acetate.  L/ead  was  also  deposited  in  a  compact  form  from 
an  alkaline  tartrate  solution  of  this  metal  in  the  presence 
of  an  alkaline  acetate. 

After  L/uckow's  experiments  upon  manganese,  little 
attention  appears  to  have  been  given  this  metal  until 
Riche  (1878)  published  his  results.  While  confirming 
the  observations  of  Luckow,  he  discovered  that  manga- 
nese was  not  only  completely  precipitated  from  the  solu- 
tion of  its  sulphate,  but  also  from  that  of  the  nitrate,  thus 
rendering  possible  an  electrolytic  separation  of  manganese 
from  copper,  nickel,  cobalt,  zinc,  magnesium,  the  alkaline 
earth,  and  the  alkali  metals.  Riche  recommended  that 
the  deposited  dioxide  be  carefully  dried,  converted  by 
ignition  into  the  protosesquioxide,  and  weighed  as  such. 
According  to  this  chemist  the  one-millionth  of  a  gram  of 
manganese,  when  exposed  to  the  action  of  the  current 


HISTORICAL.  5 1 

gave  a  distinct  rose-red  color,  perceptible  even  when 
diluted  tenfold. 

In  zinc  depositions  Riche  gave  preference  to  a  solution 
of  zinc-ammonium  acetate  containing  free  acetic  acid. 

lyUckow  was  the  first  to  mention  that  the  current  caused 
mercury  to  separate  in  a  metallic  form,  from  acid  solu- 
tions, upon  the  negative  electrode.  F.  W.  Clarke  (1878) 
used  a  mercuric  chloride  solution,  feebly  acidulated  with 
sulphuric  acid,  for  this  purpose.  The  deposition  was 
made  in  a  platinum  dish,  using  six  Bunsen  cells.  Mer- 
curous  chloride  was  at  first  precipitated,  but  it  was  gradu- 
ally reduced  to  the  metallic  form.  J.  B.  Hannay  (1873) 
had  previously  recommended  precipitating  this  metal 
from  solutions  of  mercuric  sulphate,  but  gave  no  results. 

Clarke,  also,  gave  some  attention  to  cadmium;  his 
results,  however,  were  not  satisfactory.  A  few  months 
later  the  writer  (1878)  succeeded  in  depositing  cadmium 
completely  and  in  a  very  compact  form  from  solutions  of 
its  acetate.  Upon  this  behavior  Yver  (1880)  based  his 
separation  of  cadmium  from  zinc.  Furthermore,  the 
writer  found  (1880)  that  the  deposition  of  cadmium  could 
be  made  from  solutions  of  its  sulphate,  contrary  to  an 
earlier  observation  of  Wrightson.  At  the  same  time 
copper  was  completely  separated  from  cadmium  by  elec- 
trolyzing  their  solution  in  the  presence  of  free  nitric  acid. 

A  very  successful  determination  of  both  zinc  and  cad- 
mium was  published  by  Beilstein  and  Jawein  in  1879. 
They  employed  for  this  purpose  solutions  of  the  double 
cyanides. 

Heinrich  Fresenius  and  Bergmann  (1880)  found  that 
the  electrolysis  of  nickel  and  cobalt  solutions  succeeded 
best  in  the  presence  of  an  excess  of  free  ammonia  and 
ammonium  sulphate. 


52  ELECTRO-CHEMICAL    ANALYSIS. 

Their  experience  with  silver  demonstrated  that  the  best 
results  could  be  obtained  with  solutions  containing  free 
nitric  acid,  and  by  the  employment  of  weak  currents. 

The  writer  (1880)  showed  that  if  uranium  acetate  solu- 
tions were  electrolyzed  the  uranium  was  completely  pre- 
cipitated as  a  hydrated  protosesquioxide ;  and,  further, 
that  molybdenum  could  be  deposited  as  hydrated  sesqui- 
oxide  from  warm  solutions  of  ammonium  molybdate  in 
the  presence  of  free  ammonia.  Very  promising  indica- 
tions were  obtained  with  salts  of  tungsten,  vanadium,  and 
cerium. 

In  a  more  recent  (1880)  communication  from  L/uckow, 
to  whom  we  are  indebted  for  much  that  is  valuable  in 
electrolysis,  is  given  a  full  description  of  his  observations 
in  this  field  of  analysis,  from  which  the  following  con- 
densed account  is  taken.  While  it  relates  more  particu- 
larly to  the  qualitative  behavior  of  various  compounds, 
its  importance  demands  careful  study. 

When  the  current  is  conducted  through  an  acid  solution 
of  potassium  chromate,  the  chromic  acid  is  reduced  to 
oxide;  whereas,  if  the  solution  of  the  oxide  in  caustic 
potash  be  subjected  to  a  like  treatment,  potassium  chro- 
mate is  produced.  Arsenic  and  arsenious  acid  behave 
similarly.  The  same  is  true  also  of  the  soluble  ferro-  and 
ferri-cyanides  and  nitric  acid.  In  the  presence  of  sul- 
phuric acid  ferric  and  uranic  oxides  are  reduced  to  lower 
states  of  oxidation.  Sulphates  result  in  the  electrolysis  of 
the  alkaline  sulphites,  hyposulphites,  and  sulphides,  and 
carbonates  from  the  alkaline  organic  salts.  In  short,  the 
current  has  a  reducing  action  in  acid  solutions,  and  the 
opposite  effect  in  those  that  are  alkaline.  In  the  electrol- 
ysis of  solutions  of  hydrogen  chloride,  bromide,  iodide, 
cyanide,  ferro-  and  ferri-cyanide  and  sulphide,  the  hydro- 


HISTORICAL.  53 

gen  separates  at  the  electro-negative  pole,  and  the  electro- 
negative constituents  at  the  positive  electrode.  Cyano- 
gen sustains  a  more  thorough  decomposition,  the  final 
products  being  carbon  dioxide  and  ammonia.  In  the 
electrolysis  of  ferro-  and  ferri-cyanogen  Prussian  blue 
separates  at  the  positive  electrode.  In  dilute  chloride 
solutions  hypochlorous  acid  is  the  only  product,  whereas 
chlorine  is  also  present  in  concentrated  solutions.  In 
alkaline  chloride  solutions  chlorates  are  produced  as  soon 
as  the  liquid  becomes  alkaline.  In  the  iodides  and  bro- 
mides iodine  and  bromine  separate  at  the  positive  elec- 
trode, while  bromates  and  iodates  are  formed  when  metals 
of  the  first  two  groups  are  present.  Potassium  cyanide  is 
converted  into  potassium  and  ammonium  carbonates. 
Concentrated  nitric  acid  is  reduced  to  nitrous  acid ;  how- 
ever, when  its  specific  gravity  equals  1.2,  this  does  not 
occur,  at  least  not  when  a  feeble  current  is  used.  Dilute 
nitric  acid  alone,  or  even  in  the  presence  of  sulphuric  acid, 
is  not  reduced  to  ammonia.  (See  also  Z.  f.  anorg.  Ch., 
31,  289.)  If,  however,  dilute  nitric  acid  be  present  in  a 
copper  sulphate  solution  undergoing  electrolysis,  copper 
will  separate  upon  the  negative  electrode  and  ammonium 
sulphate  will  be  formed.  Solutions  of  nitrates  containing 
sulphuric  acid  behave  analogously.  Phosphoric  acid  sus- 
tains no  change.  Silicic  acid  separates  as  a  white  mass, 
and  boric  acid,  in  crystals  uniting  to  arborescent  groups, 
at  the  positive  electrode. 

IntheBer.  d.  d.  chem.  Gesellschaft  for  1881  (Vol.  14, 
1622),  Classen  and  v.  Reiss  presented  the  first  of  a  series 
of  papers  upon  electrolytic  subjects,  which  continued 
through  subsequent  issues  of  this  publication.  Their 
early  work  was  devoted  to  the  precipitation  of  metals 
from  solutions  of  their  double  oxalates.  They  also 


54  ELECTRO-CHEMICAL   ANALYSIS. 

elaborated  excellent  methods  for  antimony  and  tin. 
Many  very  serviceable  forms  of  apparatus,  intended  for 
electrolytic  work,  were  devised  and  described  by  them, 
and  it  must  be  conceded  that  through  the  activity  of  the 
Aachen  School  electrolysis  acquired  more  importance  in 
the  eyes  of  the  chemical  public  that  it  ever  before  pos- 
sessed. The  details  of  the  more  important  methods  pro- 
posed by  Classen  and  his  co-laborers  will  receive  due 
mention  under  the  respective  metals. 

At  the  same  time  with  and  quite  independently  of 
Classen,  Reinhardt  and  Ihle  proposed  the  double  oxalates 
for  the  estimation  of  zinc  electrolytically ;  and  in  this  con- 
nection it  may  not  be  improper  to  mention  that  as  early 
as  1879,  two  years  prior  to  the  publication  of  Classen's 
first  communication,  Parodi  and  Mascazzini  (Gazetta 
chimica  italiana,  Vol.  8,  178)  announced  that  antimony 
and  iron  could  be  deposited  completely  and  in  compact 
form  by  electrolyzing  the  solutions  of  the  sulpho-salts  of 
the  former  and  the  chloride  of  the  latter  in  the  presence 
of  acid  ammonium  oxalate. 

In  1883  Wolcott  Gibbs  "  gave  an  account  of  a  method  of 
electrolysis  for  the  separation  of  metals  from  their  solu- 
tions by  the  employment  of  mercury  as  negative  elec- 
trode, the  positive  electrode  being  a  plate  of  platinum. 
Under  these  circumstances,  and  with  a  current  of  moderate 
force,  it  was  found  possible  to  separate  iron,  cobalt,  nickel, 
zinc,  cadmium,  and  copper  so  completely  from  solutions  of 
the  respective  sulphates  that  no  trace  of  metal  could  be 
detected  in  the  liquid.  In  addition  it  was  found  that  phos- 
phates of  these  metals  dissolved  in  dilute  sulphuric  acid 
were  easily  resolved  into  amalgams  and  free  acid,  and  the 
advantages  of  the  method  were  pointed  out  in  at  least  a 
certain  number  of  cases.  The  author  had  in  view  both  the 


HISTORICAL.  5  5 

determination  of  the  metal  by  the  increase  in  weight  of  the 
mercury,  and  in  particular  cases  of  the  molecule  combined 
with  the  metal,  either  by  direct  titration  or  by  known  gravi- 
metric methods."  The  experiments  were  purely  qualita- 
tive, such  being  in  the  author's  opinion  sufficient  to  estab- 
lish the  correctness  of  the  principle  involved.  "It  is  to 
be  hoped  that  the  determination  quantitatively  of  the 
electro-negative  atoms  or  molecules  united  with  the  metal 
will  also  attract  attention,  the  method  having  been  origi- 
nally intended  to  serve  the  double  purpose. ' '  This  method 
is  not  applicable  in  the  case  of  antimony  and  arsenic. 

Three  years  later  (1886)  Luckow  recommended  a  very 
similar  procedure  for  the  estimation  of  zinc. 

Moore  (1886)  also  published  new  data  upon  the  estima- 
tion of  iron,  cobalt,  nickel,  manganese,  etc.,  full  notice  of 
which  will  appear  under  these  metals. 

Whitfield  (1886)  suggested  an  indirect  determination 
of  the  halogens  electrolytically,  which  no  doubt  will  prove 
useful. 

Brand  (1889)  succeeded  in  effecting  separations  by 
utilizing  solutions  of  the  pyrophosphates  of  different 
metals. 

Smith  and  Frankel  (1889)  made  an  extended  study  of 
the  double  cyanides,  and  found  thereby  a  number  of  very 
convenient  methods  of  separation  heretofore  unrecorded. 
The  results  of  their  numerous  investigations  in  this  direc- 
tion are  given  in  detail  in  the  following  pages. 

Other  publications  relating  to  electrolysis  are  that 
of  Warwick  on  metallic  formates  (Z.  f.  anorg.  Ch.,  1, 
285),  that  of  Frankel  on  the  oxidation  of  metallic  arsen- 
ides (Ch.  News,  65,  54),  and  that  of  Vortmann  (Ber.,  24, 
2749)  upon  the  electro-deposition  of  metals  in  the  form  of 
amalgams,  together  with  a  series  of  critical  reviews  of 


56  ELECTRO-CHEMICAL    ANALYSIS. 

electrolytic  methods  by  Riidorff  in  the  Z.  f.  ang.  Ch., 
1892. 

During  the  past  eight  years  the  efforts  in  electro- 
chemical analysis  have  had  for  their  chief  purpose  the 
perfecting  of  methods.  The  absence  of  reliable  working 
conditions  necessitated  a  careful  review  of  earlier  sugges- 
tions, with  the  result  that  while  some  have  been  aban- 
doned, the  greater  number  have  been  re-enforced  and 
have  been  given  a  more  favorable  and  extended  use. 
Freudenberg  (1893)  revived  the  idea  to  which  Kiliani 
first  called  attention,  viz. :  that  by  the  application  of  suit- 
able decomposition-pressures  metal  separations  could  be 
easily  executed  in  the  electrolytic  way.  This  contribu- 
tion, published  in  the  Z.  f .  ph.  Ch. ,  12, 97,  should  be  seriously 
studied  by  all  persons  interested  in  electro-chemical  anal- 
ysis. Singularly  enough,  the  separations  therein  indi- 
cated had  been  previously  made  by  Smith  and  Frankel 
(1889),  and  the  statement  also  appears  that  by  the  use  of 
the  double  cyanides  the  field  of  separations  was  widely 
extended.  (See  also  J.  Am.  Ch.  S.,  16,  93.) 

The  direct  determination  of  the  halogens  electro- 
lytically  has  been  worked  out  by  Vortmann  (1895). 

Other  contributions  have  considered  the  availability  of 
known  electro-chemical  methods  to  technical  analysis, 
and  many,  too,  have  been  almost  wholly  controversial  in 
their  character,  so  that  they  may  be  omitted  here.  The 
literature  references  to  them  appear  in  their  appropriate 
places. 

The  preceding  paragraphs  give  a  brief  outline  of  what 
has  been  accomplished  in  the  field  of  analysis  by  electrol- 
ysis ;  for  further  information  consult  the  following  :— 

LITERATURE. — Jahrb.,  1850,  602;  C.  r.,  45,  449;  Jr.  f.  pkt.  Ch.,  73,  79; 
Chem.  Soc.  Quart.  Journ.,  13,  12;  Jahrb.,  1862,  610;  Ann.,  124,  131  ;  C.  r., 


HISTORICAL.  57 

55,  18;  Ann.,  146,  375;  Z.  f.  a.  Ch.,  3,  334;  Ding.  p.  Jr.  (1865),  231;  Z.  f.  a. 
Ch.,  8,  23;  n,  i,  9;  13,  183;  Am.  Jr.  Sc.  and  Ar.  (36  ser. ),  6,  255  ;  Z.  f.  a.  Ch., 
J5>  297  5  Ber.,  10,  1098 ;  Annales  de  Ch.  et  de  Phy.,  1878  ;  Am.  Jr.  Sc.  and  Ar., 
16,  200;  Am.  Phil.  Soc.  Pr.,  1878;  Z.  f.  a.  Ch.,  15,  303;  Am.  Ch.  Jr.,  2,  41  ; 
Berg-Hutt.  Z.,  37,  41  ;  Z.  f.  a.  Ch.,  19,  I,  314,  324;  Am.  Ch.  Jr.,  i,  341 ;  B.  s. 
Ch.  Paris,  34,  18;  Ber.,  12,  1446;  14,  1622,  2771  ;  17,  1611,  2467,  2931  ;  18, 
168,  1104,  1787  ;  19,  323;  21,  359,  2892,  2900;  Jr.  f.  pkt.  Ch.,  24,  193  ;  Z.  f.  a. 
Ch.,  18,588;  22,558;  25,113;  Ch.  News,  28,  581  ;  53,209;  Ber.,  25,  2492 ; 
Z.  f.  ph.  Ch.,  12,  97;  Ber.,  27,  2060;  Z.  f.  Elektrochem.,  2,  231,  253,  269;  Z. 
f.  a.  Ch.  (1893),  32,  424.  And  the  following  will  be  found  worthy  of  careful 
study  :  Ann.,  36,  32  ;  94,  I  ;  Z.  f.  a.  Ch.,  19,  I  ;  Berg-Hutt.  Z.,  42,  377  ;  Z.  f.  a. 

Ch.,   22,  485. 


SPECIAL  PART. 


i.  DETERMINATION    OF   THE    DIFFER- 
ENT METALS. 

COPPER. 

LITERATURE. — Gibbs,  Z.  f.  a.  Ch.,  3,  334;  Boisbaudran,  B.  s.  Ch. 
Paris,  1867,  468;  Merrick,  Am.  Ch.,  2,  136;  Wrightson,  Z.  f.  a.  Ch.,  15, 
299;  Herpin,  Z.  f.  a.  Ch.,  15,  335;  Moniteur  Scientifique  [3  ser.],  5,  41; 
Ohl,  Z.  f.  a.  Ch.,  18,  523;  Classen,  Ber.,  14,  1622,  1627;  Classen  and  v. 
Reiss,  Z.  f.  a.  Ch.,  24,  246;  25,  113;  Hampe,  Berg-Hutt.  Z.,  21,  220; 
Riche,  Z.  f.  a.  Ch.,  21,  116;  Makintosh,  Am.  Ch.  Jr.,  3,  354;  Riidorff, 
Ber.,  21,  3050;  Z.  f.  ang.  Ch.,  1892,  p.  5  ;  Luckow,Z.  f.  a.  Ch.,8,  23;  War- 
wick, Z.  f.  anorg.  Ch.,  x,  285  ;  Smith,  Am.  Ch.  Jr.,  12,  329;  Croasdale,  Jr. 
An.  Ch.,5,  133;  Foote,  Am.  Ch.  Jr.,  6,  333 ;  G.  H.  Meeker,  Jr.  An.  Ch., 
6,267;  Classen,  Ber.,  27,  2060;  Heidenreich,  Ber.,  29,  1585  ;  Regels- 
berger,  Z.  f.  ang.  Ch.,  1891,  473;  Oettel,  Ch.  Z.,  1894,  879;  Schweder, 
Berg-Hutt.  Z.,  36  (5),  II,  21;  Fernberger  and  Smith,  J.  Am.  Ch.  S.,  21, 
looi  ;  Wagner,  Z.  f.  Elektrochem. ,  2,  613;  Oettel,  Ch.  Z.  (1894),  47, 
879;  Forster  and  Seidel,  Z.  f.  anorg.  Ch.,  14,106;  Head,  Trans.  Am.  Inst. 
Mining  Engineers,  1898;  Re  v  ay,  Z.  f.  Elektrochem.,  4,  313-329;  Ullmann, 
Ch.  Z.,  22,  808;  Hollard,  C.  r.,  123,  1003  (1896);  Kollock,  J.  Am.  Ch. 
S.,  21,  923. 

Dissolve  19.6  grams  of  pure  copper  sulphate  in  water, 
and  dilute  to  i  litre.  Place  50  c.c.  of  this  solution  ( =  0.25 
gram  of  metallic  copper)  in  a  clean  platinum  dish,  pre- 
viously weighed.  Arrange  the  apparatus  as  in  the  ac- 
companying sketch  (Fig.  26),  the  voltmeter  being  to 
the  left  of  the  dish  and  the  milliamperemeter  and  the 
rheostat  to  the  right-hand  side  of  the  same;  and  having 

58 


DETERMINATION    OF    METALS COPPER. 


59 


done  this,  add  9-10  drops  of  concentrated  nitric  acid  to  the 
solution  of  the  electrolyte;  dilute  to  125  c.c.  with  water; 
heat  to  70°,  and  electrolyze  with  a  current  of  N.D100 
=  0.09  ampere  and  1.9  volts.  Cover  the  vessel  with  a 
perforated  watch-crystal  during  the  decomposition.  Four 
to  five  hours  will  suffice  for  the  precipitation.  To  ascer- 
tain when  the  metal  has  been  completely  precipitated, 
add  water  to  the  dish  ;  this  will  expose  a  clean,  platinum 


FIG.  26. 


surface,  and  if  in  the  course  of  half  an  hour  no  copper 
appears  upon  it,  the  deposition  may  be  considered  as 
finished.  Or  a  drop  of  the  liquid  may  be  removed  and 
brought  in  contact  with  a  drop  of  ammonium  hydroxide 
or  hydrogen  sulphide,  when,  if  a  blue  coloration  or  black 
precipitate  is  not  produced,  the  deposition  can  be  con- 
sidered ended. 

As  the  precipitation  has  been  made  in  an  acid  solution 
the  current  should  not  be  interrupted  until  the  acid  liquid 


6O  ELECTRO-CHEMICAL    ANALYSIS. 

has  been  removed,  for  in  many  cases  the  brief  period 
during  which  the  acid  can  act  upon  the  metal  will  be  suffi- 
cient to  cause  some  of  the  latter  to  pass  into  solution.  To 
obviate  this,  siphon  off  the  acid  liquid.  As  the  acidulated 
water  is  conveyed  away  by  the  siphon,  pour  distilled 
water  into  the  dish.  Empty  the  platinum  dish  twice  in 
this  way;  the  current  can  then  be  interrupted  without 
loss  of  copper.  Finally,  disconnect  the  dish,  wash  the 
deposit  with  hot  water  and  then  with  alcohol.  Dry  the 
precipitated  copper  at  a  temperature  not  exceeding  100° 
C. ;  an  air-bath,  an  asbestos  plate,  or  warm  iron  plate  will 
answer  for  this  purpose.  Do  not  weigh  the  dish  until  it  is 
perfectly  cold,  and  has  attained  the  temperature  of  the 
balance-room. 

In  heating  the  dish  containing  the  electrolyte,  do  not 
apply  a  direct  lamp  flame;  attach  a  circular  piece  of  thin 
sheet- asbestos  to  the  lower  side  of  the  ring,  supporting  the 
platinum  dish,  and  under  it  place  an  ordinary  Bunsen 
burner,  or  one  reduced  in  size.  Water-baths  are  not 
needed  for  heating  purposes. 

Riidorff  suggests  the  addition  of  ten  drops  of  a  saturated 
sodium  acetate  solution  to  the  acid  liquid  from  which  the 
copper  has  been  precipitated  before  interrupting  the  cur- 
rent. The  acetic  acid,  which  is  liberated,  will  not  imme- 
diately attack  the  copper,  which  can  be  at  once  washed 
and  treated  as  just  described. 

Copper  is  very  readily  precipitated  from  solutions  con- 
taining free  nitric  or  sulphuric  acid.  Hydrochloric  acid 
never  should  be  used. 

A  platinum  dish,  50  mm.  in  diameter  and  20  mm.  in 
depth,  may  be  substituted  for  the  spiral  anode.  There 
are  openings  in  the  dish  to  facilitate  circulation  and 
accelerate  the  precipitation  of  the  metal. 


DETERMINATION    OF    METALS COPPER. 


6l 


The  deposition  of  the  copper  can  also  be  made  in  a 
platinum  crucible,  or  upon  the  exterior  surface  of  the 
same.  This  is  sometimes  convenient.  Place  the  liquid 
undergoing  electrolysis  in  a  beaker  glass  (capacity  100- 
250  c.c.),  and  suspend  the  crucible  in  it  (Fig.  27),  support- 
ing it  there  by  a  tight-fitting  cork,  through  which  passes 
a  stout  copper  wire,  w,  in  connection  with  the  negative 
electrode  of  a  battery.  The  positive  electrode  is  a  plati- 


FIG.   27. 


FIG.   28. 


num  plate  projecting  into  the  liquid.  The  end  of  the 
decomposition  may  be  learned  by  pressing  down  upon  w, 
or  by  adding  water  to  the  solution  in  the  beaker.  No 
further  appearance  of  copper  on  the  newly  exposed  plati- 
num indicates  the  end  of  the  precipitation.  Raise  the 
crucible  from  the  liquid,  wash  the  copper  with  water,  then 
detach  the  vessel  carefully  from  the  cork,  and  dry  as 
already  directed. 


62  ELECTRO-CHEMICAL    ANALYSIS. 

If  the  current  be  permitted  to  act  too  long  in  the  pres- 
ence of  sulphuric  acid,  copper  sulphide  may  be  produced. 
Black  spots  on  the  surface  of  the  copper  deposit  indicate 
this. 

Instead  of  using  either  of  the  suggestions  first  offered, 
substitute  the  apparatus  of  Riche  (Fig.  28)  if  convenient. 
This  consists  in  suspending  a  crucible  within  a  crucible. 
The  sides  of  the  inner  vessel  are  perforated  so  that  the 
liquid  will  maintain  uniform  concentration.  It  is  practi- 
cally the  same  as  the  device  just  described  above. 

Engels  recommends  the  addition  of  urea  or  hydroxyl- 
amine  sulphate  to  the  copper  sulphate  solution,  as  it  seems 
to  favor  the  deposition  of  the  metal.  He,  therefore, 
proceeds  as  follows:  Add  10-15  c.c.  of  concentrated  sul- 
phuric acid  and  1.5  grams  of  hydro xylamine  sulphate,  or  i 
gram  of  urea,  to  the  salt  solution,  dilute  to  150  c.c.  with 
water,  heat  to  70°,  and  electrolyze  with  a  current  of  N.D100 
=  0.8-1.0  ampere  and  2.7-3.1  volts.  The  metal  will  be 
precipitated  in  one  and  one-half  hours. 

Copper  can  also  be  precipitated  from  the  solution  of 
ammonium-copper  oxalate.  To  this  end  the  copper  solu- 
tion (sulphate  or  chloride)  is  treated  with  an  excess  of  a 
saturated  solution  of  ammonium  oxalate  diluted  to  120 
c.c.  with  water;  heated  to  60°  and  electrolyzed  with 
N.D100  =  0.35-1.0  ampere  and  2.5  to  3.2  volts.  As  the 
metal  begins  to  separate,  and  the  original  deep  blue  color 
of  the  liquid  disappears,  add  20-30  c.c.  of  a  cold  saturated 
solution  of  oxalic  acid.  This  should  be  added  gradually 
from  a  burette.  Avoid  the  precipitation  of  insoluble  copper 
oxalate.  When  the  decomposition  is  finished,  decant  the 
solution,  and  wash  the  deposit  of  copper  repeatedly  with 
water  and  then  with  alcohol.  Dry  as  previously  directed. 
The  precipitation  is  generally  complete  after  three  hours. 


DETERMINATION    OF    METALS COPPER.  63 

Use  ferrocyanide  of  potassium  to  learn  whether  all  the 
metal  has  been  precipitated. 

E.  Wagner  recommends  the  following  procedure  in  the 
precipitation  of  copper  from  an  oxalate  solution :  Pour  the 
copper  solution  into  the  ammonium  oxalate  solution  (4 
grams  of  ammonium  oxalate  in  60  grams  of  water  for 
i  gram  of  copper  sulphate) ;  at  the  beginning  electrolyze 
with  a  current  of  0.05  ampere  for  one-half  hour,  then  in- 
troduce 5  c.c.  of  a  cold  saturated  solution  of  oxalic  acid, 
and  at  the  expiration  of  five  minutes  increase  the  current 
to  0.3  ampere.  The  temperature  of  the  electrolyte  should 
equal  60°.  In  the  following  eighty  minutes,  during  four 
intervals,  5  c.c.  of  oxalic  acid  are  added  at  each  period  and 
the  maximum  current  of  0.4  ampere  is  applied.  Two 
hours  after  the  close  of  the  circuit  neither  ammonia  nor 
potassium  ferrocyanide  will  show  the  copper  reaction  with 
the  solution.  The  liquid  should  be  siphoned  off  without 
the  interruption  of  the  current.  The  deposit  of  copper 
should  be  washed  and  dried  as  previously  indicated. 

Copper  can  also  be  determined  quite  accurately  in  solu- 
tions of  the  phosphate  in  the  presence  of  free  phosphoric 
acid,  or  in  a  formate  solution  containing  free  formic  acid. 

The  following  example  is  given  to  show  the  applicability 
of  an  acid  phosphate  solution  for  this  particular  purpose : 
To  a  solution  of  copper  sulphate  (=  0.1239  gram  of  cop- 
per) were  added  20  c.c.  of  a  solution  of  disodium  hydrogen 
phosphate  (sp.  gr.  1.0358)  and  5  c.c.  of  phosphoric  acid 
(sp.  gr.  i  .347).  It  was  then  diluted  to  225  c.c.  with  water, 
heated  to  65°,  and  electrolyzed  with  a  current  of  N.D100  = 
0.035-0.068  ampere  and  2.2-2.6  volts.  The  precipitation 
was  completed  in  six  hours.  The  deposit  of  copper 
weighed  0.1238  gram.  It  was  washed  and  dried  as  pre- 
viously directed,  p.  60. 


64 


ELECTRO-CHEMICAL    ANALYSIS. 


Rudorff  obtained  excellent  results  with  the  following 
conditions:  0.1-0.3  gram  of  metallic  copper  in  150  c.c.  of 
water,  to  which  were  added  2-3  grams  of  potassium  or 
ammonium  nitrate  and  20  c.c.  of  ammonium  hydroxide 
(0.91  sp.  gr.).  Electrolyze  at  the  ordinary  temperature 
with  a  current  of  N.D100  =  i  ampere  and  3.3-3.6  volts. 
It  is  claimed  that  by  observing  the  preceding  conditions 
copper  can  be  fully  precipitated  in  the  presence  of  chlo- 
rides. An  excess  of  acetic  acid  should  be  added  to  the 
solution  before  the  current  is  interrupted. 


FIG.  29. 


Oettel  remarks  on  the  precipitation  of  copper  from 
ammoniacal  solutions  that  the  metal  can  be  quantitatively 
deposited  from  a  slightly  ammoniacal  liquid,  containing 
ammonium  nitrate,  with  a  current  density  of  0.07-0.27 
ampere  per  square  decimetre.  When  ammonium  nitrate 
is  absent  and  the  quantity  of  ammonia  is  large,  the  metal 
deposits  become  spongy.  He  found  the  most  satisfactory 
concentration  to  be  0.8  gram  of  copper  for  100  c.c.  of 
liquid  when  using  a  wire-form  anode  with  a  cylinder  or 
cone  as  cathode  (Fig.  29).  Chlorine,  zinc,  arsenic,  and 
small  amounts  of  antimony  were  without  deleterious 


DETERMINATION    OF    METALS COPPER.  65 

effect.     In  the  presence  of  lead,  bismuth,  mercury,  cad- 
mium, and  nickel  the  results  were  high. 

Moore  advises  dissolving  the  recently  precipitated  cop- 
per sulphide,  obtained  in  the  ordinary  course  of  analysis, 
in  potassium  cyanide;  and,  after  the  addition  of  an  excess 

FIG.  30. 


of  ammonium  carbonate,   electrolyzes   the   warm   (70°) 
solution. 

.  In  this  laboratory  it  was  observed  that  the  electrolysis 
can  be  best  and  most  satisfactorily  executed  by  dissolving 
the  sulphide  in  as  small  a  volume  of  potassium  cyanide  as 
possible,  diluting  to  150  c.c.  with  water,  heating  to  65°, 


66 


ELECTRO-CHEMICAL    ANALYSIS. 


and  electrolyzing  with  N.D100  =  0.15-0.8  ampere  and 
3-4.5  volts.  The  metal  will  be  fully  precipitated  in  from 
two  to  three  hours. 

In  the  analysis  of  commercial  copper  L/uckow  employed 


FIG.  31. 


the  apparatus  pictured  in  Fig.  30.  The  beaker  con- 
tains the  electrolyte,  and  the  metal  is  precipitated  upon 
the  cylinder  of  platinum.  It  is  a  very  satisfactory 
device  for  almost  any  kind  of  electrolytic  work.  Either 
one  of  the  arrangements  pictured  in  Figs.  31  and  32  will 


DETERMINATION  OF  METALS COPPER.        67 


FIG.  32. 


68  ELECTRO-CHEMICAL    ANALYSIS. 

answer  for  the  same  purpose.  The  platinum  gauze 
cathode  in  Fig.  32  is  much  favored  by  analysts.  An 
anode  of  similar  material  and  form  can  be  used  to  advan- 
tage. To  calculate  the  approximate  surface  of  a  cylin- 
drical gauze  cathode  use  the  formula 

S=7r<t  2^  nib 

in  which  d  is  the  diameter  of  the  wire,  n  the  number  of 
meshes  per  square  centimetre,  /  the  length  and  b  the 
width  of  the  strip  of  gauze  used  (height  of  the  cylinder). 
(Winkler,  Ber.,  32,  2192.) 


CADMIUM. 

LITERATURE. — Ber.,  n,  2048;  Smith,  Am.  Phil.  Soc.  Pr.,  1878;  Clarke, 
Z.  f.  a.  Ch.,  18,  104;  Beilstein  and  Jawein,  Ber.,  12,  759;  Smith,  Am. 
Ch.  Jr.,  2,  42;  Luckow,  Z.  f.  a.  Ch.,  19,  16  ;  Wrightson,  Z.  f.  a.  Ch.,  15, 
303;  Classen  and  v.  Reiss,  Ber.,  14,  1628;  Warwick,  Z.  f.  anorg.  Ch., 
i,  258;  Moore,  Ch.  News,  53,  209  ;  Smith,  Am.  Ch.  Jr.,  12,  329;  Vortmann, 
Ber.,  24,  2749;  Riidorff,  Z.  f.  ang.  Ch.,  Jahrg.  1892;  Classen,  Ber.,  27, 
2060;  Heidenreich,  Ber.,  29,  1586;  Wallace  and  Smith,  J.  Am.  Ch.  S., 
19,  870;  ibid.,  20,  279;  Balachowsky,  C.  r.,  131,  384;  Miller  and  Page, 
Z.  f.  anorg.  Ch.,  28,  233;  Kollock,  J.  Am.  Ch.  S.,  21,  911;  Avery  and 
Dales,  J.  Am.  Ch.  S.,  19,  380. 

Cadmium  can  be  determined  electrolytically  as  readily 
as  copper.  Prepare  a  solution  of  the  chloride  or  sulphate 
of  definite  strength.  Remove  50  c.c.  to  a  suitable, 
weighed  platinum  vessel.  Add  one  gram  of  pure  potas- 
sium cyanide;  dilute  with  water  to  125  c.c.,  heat  to 
60°,  and  electrolyze  with  N.D100  =  0.06  ampere  and  3.2 
volts.  The  metal  will  be  completely  deposited  in  five 
hours,  or  the  decomposition  may  be  begun  in  the  evening 
and  by  morning  the  metal  will  be  fully  precipitated.  To 
ascertain  whether  the  precipitation  is  complete,  raise  the 


DETERMINATION    OF    METALS CADMIUM.  69 

level  of  the  liquid  in  the  platinum  dish.  In  washing,  it 
will  not  be  necessary  to  siphon  off  the  supernatant  liquid ; 
it  can  be  poured  off,  after  interruption  of  the  current, 
without  loss  of  metal  from  re-solution.  Wash  the  deposit 
with  cold  and  hot  water;  also  with  alcohol  and  ether. 
Dry  upon  a  warm  iron  plate  (temperature  not  exceeding 
100°  C.). 

This  metal  can  be  deposited  from  the  solution  of  its 
phosphate  in  phosphoric  acid.  The  conditions  that  follow 
gave  very  satisfactory  results;  a  current  of  N.D100  =  0.06 
ampere  and  3-7  volts  acted  upon  0.1656  gram  of  cadmium 
as  sulphate,  30  c.c.  of  sodium  phosphate  (1.0358  sp.  gr.), 
and  ij  c.c.  of  phosphoric  acid  (sp.  gr.  1.347).  The  total 
dilution  equaled  100  c.c.  The  temperature  of  the  solution 
was  50°.  The  precipitated  cadmium  weighed  (a)  0.1654 
gram  and  (6)  o.  1657  gram.  The  current  for  the  last  hour  of 
the  decomposition  should  be  increased  and  the  deposit 
be  washed  before  breaking  the  current. 

Cadmium  may  also  be  precipitated  from  a  solution  of 
its  sulphate  containing  a  small  amount  of  free  sulphuric 
acid  (2  c.c.  H2SO4,  sp.  gr.  1.09  for  b.i  gram  of  cadmium). 
Heat  to  50°  and  electrolyze  with  N.D100  =  0.15  ampere 
and  2.5  volts.  Siphon  off  the  acid  liquid  before  inter- 
rupting the  current.  Treat  the  deposit  as  previously 
directed. 

Cadmium  can  also  be  deposited  quite  readily,  and  in  a 
crystalline  form,  from  its  acetate  solution.  An  example 
will  indicate  the  proper  conditions  for  a  successful  deter- 
mination: 0.1329  gram  of  cadmium  oxide  was  dissolved 
in  acetic  acid,  the  solution  was  evaporated  to  dry  ness,  and 
the  residue  dissolved  in  30  c.c.  of  water.  The  liquid  was 
then  heated  to  50°  and  electrolyzed  with  a  current  of  0.02 
ampere  for  37  sq.  cm.  of  cathode  surface  and  a  pressure  of 


7O  ELECTRO-CHEMICAL    ANALYSIS. 

3.5  volts.  The  metal  was  completely  precipitated  in  four 
hours.  It  was  crystalline  and  adherent.  The  acid  liquid 
should  be  siphoned  off  without  interrupting  the  current. 
Good  results  can  be  obtained  and  the  period  of  precipita- 
tion be  reduced  by  adding  i  gram  of  ammonium  acetate 
to  the  solution  after  the  current  has  acted  for  an  hour. 
When  the  precipitation  is  completed,  detach  the  dish, 
wash  the  deposited  metal  first  with  warm  water,  then  with 
absolute  alcohol,  and  finally  with  ether.  Dry  upon  a 
moderately  warm  plate. 

Balachowsky,  in  precipitating  cadmium,  makes  use  of  a 
silver-coated  platinum  dish.  Dissolve  from  1.5  to  2 
grams  of  cadmium  sulphate  in  100  c.c.  of  water,  add  5 
c.c.  of  acetic  acid  for  every  gram  of  salt,  heat  to  60°  and 
electrolyze  with  a  current  of  0.004  ampere  per  sq.  cm.  and 
2.8  volts.  Later  increase  the  current  to  0.006  ampere  and 
3.5  volts.  The  deposited  metal  should  be  treated  as 
already  described. 

The  same  chemist  also  obtained  very  satisfactory  re- 
sults by  adding  formaldehyde,  acetaldehyde,  or  urea  to 
the  solution  of  cadmium  sulphate.  The  liquid  was  then 
heated  to  60°  and  electrolyzed  with  a  current  of  2.5-3.3 
volts*  and  0.003  to  0.006  ampere  per  sq.  cm. 

If  desired,  the  metal  can  also  be  precipitated  from  the 
solution  of  the  double  oxalate  of  ammonium  and  cadmium 
(see  Copper),  or  from  a  formate  solution  in  the  presence  of 
free  formic  acid. 

When  using  the  oxalate  solution,  add  to  it  for  every  0.3 
to  0.4  gram  of  sulphate,  10  grams  of  ammonium  oxalate, 
dilute  to  1 20  c.c.  with  water,  heat  to  75°,  and  electrolyze 
with  N.D100  =  0.5-1.5  amperes  and  3-3.5  volts.  The  time 
necessary  for  complete  precipitation  will  be  three  and 
one-half  hours. 


DETERMINATION    OF    METALS CADMIUM.  71 

Avery  and  Dales  employed  the  formate  solution.  Their 
recommendation  is :  Add  6  c.c.  of  formic  acid  (sp.  gr.  1.20) 
to  the  solution  of  cadmium  sulphate,  then  potassium 
carbonate  until  a  slight  permanent  precipitate  is  formed, 
which  is  just  dissolved  in  formic  acid,  after  which  i  c.c.  of 
the  same  acid  is  introduced,  the  liquid  diluted  to  150  c.c. 
and  electrolyzed  with  N.D100  =  0.15-0.20  ampere  and 
2.6-3.4  volts. 

Vortmann  has  determined  several  metals  quite  satis- 
factorily in  the  form  of  amalgams.  In  applying  his 
recommendation  to  cadmium,  add  to  the  solution  of 
its  salt  a  solution  of  mercuric  chloride  and  5  grams 
of  ammonium  oxalate.  Effect  the  solution  of  the  latter 
salt  without  the  aid  of  heat.  This  procedure  is  only  good 
when  small  amounts  of  cadmium  are  present;  cadmium 
ammonium  oxalate  is  not  very  soluble.  The  current  em- 
ployed for  the  precipitation  should  at  the  very  beginning 
of  the  decomposition  equal  from  0.6  to  0.8  ampere.  When 
the  amalgam  of  mercury  and  cadmium  commences  to 
separate  reduce  the  current  to  0.3  ampere,  but  gradually 
increase  it  until  at  the  end  of  the  decomposition  it  has  its 
initial  strength.  If  the  quantity  of  cadmium  exceeds  0.3 
gram,  let  the  solution  undergoing  electrolysis  be  ammoni- 
acal.  To  this  end  add  tartaric  acid  (3  grams)  and  an 
excess  of  ammonia  to  the  liquid  containing  the  mercury 
and  the  cadmium.  Dilute  to  200  c.c.  with  water.  Allow 
the  current  to  act  until  a  portion  of  the  liquid  remains 
clear  when  tested  with  ammonium  sulphide. 

In  the  usual  course  of  gravimetric  analysis  cadmium  is 
obtained  as  sulphide.  To  prepare  it  for  electrolysis  dis- 
solve the  same  in  nitric  acid,  and  after  expelling  the  excess 
of  the  latter,  add  a  small  amount  of  potassium  hydroxide 
(sufficient  to  precipitate  the  cadmium),  and  follow  this 


72  ELECTRO-CHEMICAL    ANALYSIS. 

with  an  excess  of  potassium  cyanide   (i   to  2  grams). 
Proceed  further  as  already  directed. 


MERCURY. 

LITERATURE.— Ber.,  6,  270;  Clarke,  Am.  Jr.  Sc.  and  Ar.,  16,  200; 
Classen  and  Ludwig,  Ber.,  19,  323;  Hoskinson,  Am.  Ch.  Jr.,  3,  209; 
Smith  and  Knerr,  ibid.,  8,  206;  Smith  and  Frankel,  Am.  Ch.  Jr.,  u,  264; 
Smith,  Jr.  An.  Ch.,  5,  202  ;  Vortmann,  Ben,  24,  2749;  Brandt,  Z.  f.  a. 
Ch.,  1891,  p.  202;  Rudorff,  Z.  f.  ang.  Ch.,  1892,  p.  5  ;  Eisenberg,  Thesis, 
Heidelberg,  1895;  Schmucker,  J.  Am.  Ch.  S.,  15,  204;  Frankel,  Jr.  Fr. 
Ins.,  1891;  Rising  and  Lenher,  Berg-Hutt.  Z.,  55,  175;  Wallace  and 
Smith,  J.  Am.  Ch.  S.,  18,  169;  Fernberger  and  Smith,  J.  Am.  Ch.  S., 
21,  1006;  Kollock,  J.  Am.  Ch.  S.,  21,  911. 

In  preparing  solutions  for  experimental  purposes,  use 
either  mercuric  nitrate  or  chloride.  To  a  definite  portion 
of  such  a  solution  add  3  c.c.  of  concentrated  nitric  acid 
dilute  to  125  c.c.,  heat  to  70°,  and  electrolyze  with  a  cur 
rent  of  N.D100  =  0.06  ampere  and  2  volts.  The  metal  will 
be  fully  precipitated  in  four  hours.  The  deposit  will  be 
drop-like  in  appearance.  The  acid  liquid  must  be  re- 
moved before  the  interruption  of  the  current  occurs,  or 
sodium  acetate  should  be  added;  then  the  liquid  can  be 
decanted  without  the  possibility  of  loss  from  resolu- 
tion of  the  mercury  (Rudorff). 

A  mercuric  chloride  solution,  feebly  acidulated  with 
sulphuric  acid  (0.5  c.c.  of  sulphuric  acid),  diluted  to  125 
c.c.,  heated  to  65°,  and  electrolyzed  with  a  current  of 
N.D100  =  0.4-0.6  ampere  and  3.5  volts,  will  yield  all  its 
metal  in  one  hour.  Always  wash  the  deposited  metal 
with  cold  water.  Rudorff  adds  the  following  substances 
to  the  liquid  containing  the  mercury  salt :  0.5  gram  of  tar- 
taric  acid  and  10  c.c.  of  ammonium  hydroxide  (sp.  gr. 
0.91),  or  5  c.c.  of  nitric  acid,  10  c.c.  of  a  saturated  solu- 


DETERMINATION    OF    METALS MERCURY.  73 

tion  of  sodium  pyrophosphate,  and  10  c.c.  of  ammonium 
hydroxide.  A  current  of  0.02  ampere  will  precipitate 
the  mercury  in  a  compact,  adherent  form. 

From  experiments  made  in  this  laboratory  the  writer 
prefers  and  would  especially  recommend  solutions  of  the 
double  cyanide  of  mercury  and  potassium  for  the  electro- 
lytic deposition  of  mercury.  To  the  mercury  salt  solu- 
tion add  i  gram  of  pure  potassium  cyanide  for  every  o.  i— 
0.2  gram  of  metal,  dilute  with  water  to  100  c.c.,  heat  to 
65°,  and  electrolyze  with  a  current  of  N.D100  =  0.02-0.07 
ampere  and  1.6-3.2  volts.  As  much  as  0.25  gram  of 
metal  can  be  deposited  in  three  hours.  This  procedure 
requires  no  further  attention  after  it  is  once  set  in  opera- 
tion. The  deposit  is  always  compact,  and  gray  in  color. 
Use  water  only  in  washing  it,  for  alcohol  seems  to  detach 
some  of  the  metallic  film. 

Classen  recommends  the  double  oxalate  solution  for 
electrolytic  purposes,  and  to  that  end  adds  to  the  mer- 
curic chloride  solution  from  4  to  5  grams  of  ammonium 
oxalate,  dilutes  with  water  to  120  c.c.,  and  electrolyzes  at 
29-37°  with  a  current  of  N.D100  =  i  ampere  and  4.05-4.7 
volts.  The  mercury  comes  down  in  a  perfectly  adherent 
form,  the  time  depending  entirely  upon  the  pressure. 

The  precipitation  is  also  very  satisfactory  in  a  phos- 
phoric acid  solution,  as  is  seen  in  the  following  example: 
To  a  solution,  containing  0.1159  gram  of  mercury,  were 
added  30  c.c.  of  sodium  phosphate  (sp.  gr.  1.038)  and  5 
c.c.  of  phosphoric  acid  (sp.  gr.  1.347),  after  which  it  was 
diluted  to  175  c.c.  with  water,  heated  to  50°,  and  electro - 
lyzed  for  four  hours  with  a  current  of  N.D100  =  0.04  am- 
pere and  1.6  volts.  The  deposit  of  mercury  weighed 
o.i  162  gram.  It  was  treated  in  the  usual  manner. 

In  general  analysis  mercury  is  frequently  obtained  as 
7 


74  ELECTRO-CHEMICAL    ANALYSIS. 

sulphide.  Its  determination  in  this  form  requires  time 
and  exceeding  care.  It  is,  however,  soluble  in  the  fixed 
alkaline  sulphides  containing  free  alkali.  The  writer  has 
discovered  that  such  a  solution  can  be  electrolyzed  with- 
out difficulty ;  the  mercury  is  deposited  from  it  in  a  very 
compact  form.  An  actual  analysis  conducted  in  this 
laboratory  will  best  present  the  proper  conditions  for  a 
successful  determination:  20  c.c.  of  a  sodium  sulphide 
solution  (sp.  gr.  1.19)  were  added  to  a  mercuric  chloride 
solution  (=-  0.1903  gram  of  mercury),  and  the  whole  then 
diluted  to  125  c.c.  with  water.  This  was  acted  upon  with 
a  current  of  N.D100  =  o.n  ampere  and  2.5  volts  for  five 
hours.  The  temperature  of  the  solution  was  70°.  The 
weight  of  the  precipitated  mercury  was  0.1902  gram.  It 
was  further  treated  as  advised  in  the  preceding  para- 
graphs. It  is  best  to  use  a  platinum  dish  as  the  negative 
electrode  and  a  platinum  spiral  (p.  59)  for  the  anode. 
Dry  the  deposit  on  a  moderately  warm  plate  or  over 
sulphuric  acid. 

Several  determinations  of  mercury  in  cinnabar  were 
made  to  test  the  general  applicability  of  the  method. 
Samples  of  the  mineral,  analyzed  in  the  usual  gravimetric 
way,  showed  the  presence  of  85.40  percent,  of  metallic 
mercury.  Portions  of  the  same  mineral  were  weighed 
out  in  platinum  dishes  and  after  solution  in  20  to  25  c.c. 
of  sodium  sulphide  of  the  specific  gravity  previously  men- 
tioned, were  diluted  with  water  to  125  c.c.  and  electro- 
lyzed at  70°,  with  the  conditions  recorded  in  the  preceding 
paragraph.  The  period  of  time  allowed  for  the  precipita- 
tions never  exceeded  three  hours.  The  results  were : — 

CINNABAR,  IN  MERCURY,  IN  MERCURY 

GRAMS.  GRAMS.  PERCENTAGE. 

0.2167  0.1850  85.37 

0.2432  0.2077  85.40 


DETERMINATION    OF    METALS BISMUTH.  75 

The  platinum  dishes  were  covered  during  the  electro- 
lytic decomposition.  It  should  be  done  in  the  determi- 
nation of  every  metal.  Its  purpose  here  was  to  prevent 
evaporation,  thereby  exposing  a  rim  of  metal,  which,  if  in 
part  not  volatilized,  would  yet  be  changed  to  mercury 
sulphide,  indicated  by  a  dark-colored  film. 


BISMUTH. 

LITERATURE. — Luckow,  Z.  f.  a.  Ch.,  19,  16  ;  Classen  and  v.  Reiss, 
Ber.,  14,  1622;  Thomas  and  Smith,  Am.  Ch.  Jr.,  5,  114;  Moore,  Ch. 
News,  53,  209;  Smith  and  Knerr,  Am.  Ch.  Jr.,  8,  206;  Schucht,  Z.  f.  a. 
Ch.,  22,  492;  Eliasberg,  Ber.,  19,  326;  Brand,  Z.  f.  a.  Ch.,  28,  596;  Vort- 
mann,  Ber.,  24,  2749;  Riidorff,  Z.  f.  ang.  Ch.,  1892,  199;  Smith  and 
Saltar,  Z.  f.  anorg.  Ch.,  3,  418  ;  Smith  and  Moyer,  J.  Am.  Ch.  S.,  15,  28  ; 
ibid.,  15,  101 ;  Wieland,  Ber.,  17,  1612  ;  Smith  and  Knerr,  Am.  Ch.  Jr.,  8, 
206;  Schmucker,  Z.  f.  anorg.  Ch.,  5,  199;  J.  Am.  Ch.  S.,  15,  203;  Kol- 
lock,  J.  Am.  Ch.  S.,  21,  925  ;  Wimmenauer,  Z.  f.  anorg.  Ch.,  27,  I  ;  Brunck, 
Ber.,  35,  1871  ;  Balachowsky,  C.  r.,  131,  179-182. 


The  electrolytic  determination  of  bismuth  has  received 
much  attention.  Numerous  electrolytes  have  been  sug- 
gested. Most  of  them  have  failed  in  that  the  deposits  of 
metal,  unless  very  small  in  amount,  have  almost  invaria- 
bly been  dark  in  color  and  have  shown  a  tendency  to 
sponginess.  Yet  they  were  in  nearly  all  cases  adherent. 
There  has  been  an  additional  objection  in  many  of  the 
methods  to  the  separation  of  peroxide  upon  the  anode. 
In  short,  the  appearance  of  bismuth  at  both  poles  has 
been  very  disturbing.  For  these  reasons  many  of  the 
earlier  suggestions  have  been  abandoned,  and  will  be 
omitted  from  the  present  text. 

Vortmann  prefers  the  amalgam  method,  in  accordance 
with  which  dissolve  0.5  gram  of  bismuth  trioxide  and  2 


76  ELECTRO-CHEMICAL    ANALYSIS. 

grams  of  mercuric  oxide  in  sufficient  nitric  acid  for  the 
purpose,  dilute  with  water  to  150  c.c.,  and  at  the  ordinary 
temperature  electrolyze  with  N.D100  =  i  ampere  and  3.5 
volts.  The  amalgam,  when  the  ratio  is  4Hg  to  iBi, 
will  be  silver- white  in  color.  It  should  be  washed  without 
interrupting  the  current,  then  carefully  dried  and  weighed. 
The  method  is  said  to  be  especially  well  adapted  for  the 
precipitation  of  large  quantities  of  bismuth. 

Wimmenauer  has  reviewed  the  different  methods  pro- 
posed from  time  to  time,  and  from  his  experience  recom- 
mends the  following  procedure:  Dissolve  0.1-0.3  gram 
of  bismuth  nitrate  in  2-4  c.c.  of  a  glycerol  solution  (i  part 
of  commercial  glycerol  and  2  parts  of  water),  dilute  with 
water  to  150  c.c.,  and  electrolyze  at  50°,  in  a  roughened 
dish,  with  a  current  of  N.D100  =  o.  i  ampere  and  2  volts. 
The  anode  is  rotated  during  the  decomposition.  This  can 
be  accomplished  by  a  small  electric  motor,  as  shown  in 
Fig.  33.  The  rotation  is  supposed  to  prevent  the  forma- 
tion of  peroxide,  because  the  latter,  by  the  movement 
of  the  anode,  is  immediately  brought  in  contact  with 
dilute  nitric  acid,  in  which  it  dissolves.  When  the  anode 
is  at  rest,  a  protective  layer  of  gas  forms  about  it,  and  this 
is  favorable  to  the  deposition  of  peroxide.  The  objection 
may  be  made  that  this  plan  is  involved  and  cannot  be 
readily  duplicated  in  practical  work. 

A.  L/.  Kammerer,  who  has  very  recently  made  an  ex- 
haustive study  on  the  electrolytic  determination  of  bis- 
muth in  this  laboratory,  where  he  has  tried  every  form  of 
cathode  and  anode  with  varying  electrolytes,  concludes 
that  the  following  conditions  may  be  relied  upon  to  yield 
satisfactory  results:  0.10-0.15  gram  of  metal  in  i  c.c.  of 
nitric  acid  (sp.  gr.  1.42),  2  c.c.  of  sulphuric  acid  (sp.  gr. 
1.84),  i  gram  of  potassium  sulphate,  150  c.c.  total  dilution, 


DETERMINATION    OF    METALS BISMUTH. 


77 


N.D100  =  0.02  ampere,  V        1.8.     Temperature,  45°-5o°; 
time,  6-7  hours. 

The  current  should  be  increased  the  last  hour  to  0.15 
ampere.  Heat  is  absolutely  essential  in  order  to  get  a 
bright  metallic  deposit  of  metal.  The  deposit  should  be 
washed  without  interrupting  the  current,  just  as  has  been 
recommended  with  other  metals  when  precipitated  from 


FIG.  33. 


an  acid  solution.  Close-fitting  cover-glasses  should  al- 
ways be  used  to  reduce  the  evaporation  to  a  minimum. 
The  metal  seemed  to  be  deposited  as  well  upon  smooth  as 
upon  roughened  surfaces. 

The  many  successful  determinations  made  in  accord- 
ance with  the  directions  just  described  indicate  that  the 
method  is  perhaps  the  best  which  has  ever  been  applied  in 
the  case  of  this  particular  metal. 


78  ELECTRO-CHEMICAL   ANALYSIS. 

In  determining  bismuth  Balachowsky  keeps  in  view  the 
following  points:  (a)  A  slightly  acid  solution;  (6)  the 
absence  of  large  amounts  of  the  halogens ;  (c)  the  use  of  a 
low  current  density  (not  exceeding  0.06  ampere  per  square 
decimetre) ;  (d)  a  roughened  dish ;  (e)  the  addition  of  urea 
or  aldehyde;  and  offers  this  example:  0.06-1.7  grams  of 
bismuth  sulphate,  5-7  c.c.  of  nitric  acid,  150  c.c.  of  water, 
3.5-5  grams  of  urea;  N.D100  =  0.04-0.06  ampere  and  1-2 
volts.  Temperature,  6o°-7o°;  time,  6-10  hours. 

When  it  is  necessary  to  use  an  alkaline  citrate  or  citric 
acid  solution  in  the  precipitation  of  bismuth,  observe  the 
following  conditions:  0.1822  gram  of  bismuth,  3  grams  of 
citric  acid,  125  c.c.  total  dilution;  N.D100  =  0.03  ampere, 
volts  =  2.  Temperature,  65°;  time,  6  hours.  0.1820 
gram  of  bismuth  was  found.  Weigh  the  anode  before  and 
after  the  electrolysis. 


LEAD. 

LITERATURE.  —  Kiliani,  Berg-Hutt.  Z.,  1883,  253;  Luckow,  Z.  f. 
a.  Ch.,  19,  215;  Riche,  Ann.  de  Chim.  et  de  Phys.  [5  ser.],  13,  508;  Z.  f.  a. 
Ch.,  21,  117;  Classen,  ibid.t  257;  Hampe,  Z.  f.  a.  Ch.,  13,  183;  May, 
Am.  Jr.  Sc.  and  Ar.  [3  ser.],  6,  255;  also  Z.  f.  a.  Ch.,  14,  347;  Parodi  and 
Mascazzini,  Ber.,io,  1098;  Z.  f.  a.  Ch.,  16,  469;  18,588;  Riche,  Z.  f.  a. 
Ch.,  17,219;  Schucht,  Z.  f.  a.  Ch.,  21,  488;  Tenny,  Am.  Ch.  Jr.,5,  413; 
Smith,  Am.  Phil.  Soc.  Pr.,  24,  428 ;  Vortmann,  Ber.,  24,  2749;  Riidorff, 
Z.  f.  ang.  Ch.,  1892,  p.  198;  Warwick,  Z.  f.  anorg.  Ch.,  I,  258;  Classen, 
Ber.,  27,  163;  Kreichgauer,  Ber.,  27,  315;  Z.  f.  anorg.  Ch.,  9,  89;  Clas- 
sen, Ber.,  27,  2060;  Medicus,  Ber.,  25,  2490;  Neumann,  Ch.  Z.  (1896), 
20,  381;  Hollard,  B.  s.  Ch.  Paris,  19,  911;  Linn,  J.  Am.  Ch.  S.,  24, 
435  ;  Marie,  Ch.  Z.,  24,  341,  480;  Nissenson  and  Neumann,  Ch.  Z.,  19, 
"43- 

The  metal  may  be  obtained  by  electrolyzing  solutions 
of  the  double  oxalate  (see  Copper  and  Cadmium),  the 
acetate,  the  oxide  in  sodium  hydroxide,  or  the  phosphate 


DETERMINATION    OF    METALS LEAD.  79 

dissolved  in  the  latter  reagent  or  in  phosphoric  acid  of  1.7 
specific  gravity.  While  the  metal  separates  well  from 
either  one  of  these  solutions,  difficulty  is  experienced  in 
drying  the  deposit,  for  the  moist  metal  almost  invariably 
suffers  a  partial  oxidation,  thus  rendering  the  results  high. 
The  deposit  can  be  dried,  without  oxidation,  in  an  atmos- 
phere of  hydrogen,  but  for  the  inexperienced  operator 
this  procedure  offers  little  satisfaction.  It  is,  therefore, 
better  to  utilize  the  tendency  of  lead  to  separate,  from 
acid  solutions,  as  the  dioxide.  For  trial  purposes  make 
up  a  definite  volume  of  lead  nitrate.  Electrolyze  several 
portions  (=  o.  i  gram  lead  each)  in  a  platinum  dish  con- 
nected with  the  anode,  using  a  current  of  N.D100  =  1.5-1.7 
amperes  and  2.36  to  2.41  volts.  The  volume  of  the  elec- 
trolyte should  be  100  c.c.  and  its  temperature  5o°-6o°.  In 
order  that  the  lead  may  be  precipitated  wholly  as  dioxide 
upon  the  positive  electrode  and  none  in  metallic  form 
upon  the  cathode,  it  is  necessary  that  the  solution  being 
analyzed  should  contain  20  c.c.  of  nitric  acid  of  specific 
gravity  1.35-1.38.  This  quantity  of  acid  is  required  when 
lead  alone  is  present  in  solution.  Chlorides  must  be  ab- 
sent. In  the  presence  of  other  metals  the  complete  depo- 
sition of  the  lead  as  dioxide  occurs  with  even  less  acid. 
At  the  end  of  the  precipitation  siphon  off  the  acid  liquid 
and  wash  in  the  dish,  then  dry  the  deposit  at  i8o°-i9o°  C., 
and  weigh.  The  weight  multiplied  by  0.866  gives  the 
quantity  of  metallic  lead  present.  The  deposit  can  be 
readily  dissolved  in  nitric  acid  to  which  oxalic  acid  is 
added,  or  cover  it  with  dilute  nitric  acid  and  insert  a  rod 
of  zinc  or  copper.  Reference  to  the  literature  shows  that 
May  preferred,  after  drying  the  deposit,  to  carefully 
ignite  it  and  finally  weigh  as  lead  oxide  (PbO).  This 
precipitation  of  lead  as  dioxide  affords  an  excellent 


8O  ELECTRO-CHEMICAL   ANALYSIS. 

method  by  which  to  separate  it  from  other  metals,  e.  g., 
mercury,  copper,  cadmium,  silver,  and  all  those  soluble 
in  nitric  acid,  or  those  which,  in  a  nitric  acid  solution,  are 
deposited  upon  the  cathode. 

Use  in  these  determinations  a  Classen  dish,  the  inner 
surface  of  which  has  been  roughened  by  having  had  a  sand 
blast  projected  against  it.  The  deposition  of  the  dioxide 
will  be  much  accelerated;  e.  g.,  a  few  hours  (4-5)  will  be 
sufficient  for  the  precipitation  of  as  much  as  4  grams  of 
dioxide  upon  100  cm2  surface  with  a  current  of  1.5  am- 
peres. Wash  with  water  and  alcohol,  then  dry  as  pre- 
viously directed. 

The  presence  of  arsenic  in  the  solution  lowers  the  lead 
results.  When  its  quantity  is  very  trifling  the  discrep- 
ancy may  be  disregarded.  Selenium  has  a  similar  effect. 

L/ead  dioxide,  like  manganese  dioxide  (p.  95),  is  not 
separated  from  solutions  containing  an  excess  of  an 
alkaline  sulphocyanide,  and  if  already  precipitated  as 
dioxide,  will  redissolve  upon  the  addition  of  the  sulpho- 
cyanide. 

In  the  analysis  of  lead  ores  Nissenson  and  Neumann 
dissolve  0.5  gram  of  the  material  in  30  c.c.  of  nitric  acid  of 
1.4  specific  gravity,  boil,  dilute  with  water,  filter  into  a 
platinum  dish,  and  electrolyze  at  6o°-7o°  with  a  current 
of  N.D100  =  i  ampere  and  2.5  volts.  The  dioxide  is 
washed  and  dried  as  indicated  above.  One  hour  is  suffi- 
cient for  the  precipitation. 

The  suggestion  made  by  Vortmann  that  lead  should  be 
precipitated  as  an  amalgam  is  not  feasible,  owing  to  cer- 
tain difficulties.  His  method,  however,  will  serve  for  the 
separation  of  the  lead  from  a  few  metals. 


DETERMINATION    OF    METALS SILVER. 


SILVER. 

LITERATURE. — Luckow,  Ding.  p.  Jr.,  178,  43;  Z.  f.  a.  Ch.,  19,  15; 
Fresenius  and  Bergmann,Z.  f.  a.  Ch.,  19,  324;  Krutwig,  Ber.,  15,  1267  ; 
Schucht,  Z.  f.  a.  Ch.,  22,  417  ;  Kinnicutt,  Am.  Ch.  Jr.,  4,  22  ;  Rudorff , 
Z.  f.  ang.  Ch.,  Jahrg.  1892,  p.  5;  Eisenberg,  Thesis,  Heidelberg,  1895; 
Smith,  Am.  Ch.  Jr.,  12,  335  ;  Ful weiler  and  Smith,  J.  Am.  Ch.  S.,  23,  583. 

The  experiments  of  L/uckow  showed  that  this  metal 
could  be  deposited  from  solutions  containing  as  high  as 
eight  to  ten  per  cent,  of  free  nitric  acid.  The  deposit  was 
spongy,  and  there  was  a  simultaneous  deposition  of  silver 
peroxide  at  the  anode.  This  was,  however,  prevented  by 
adding  to  the  solution  some  glycerol,  lactic  or  tartaric  acid. 
A  voluminous  mass  was  also  obtained  from  silver  solutions, 
containing  an  excess  of  ammonium  hydroxideor  carbonate, 
and  peroxide  appeared  at  the  same  time  upon  the  anode. 

Fresenius  and  Bergmann,  who  have  given  the  electrol- 
ysis of  acid  solutions  of  silver  particular  study,  observed 
that  the  tendency  of  the  metal  to  sponginess  is  most 
marked  when  the  electrolyte  is  concentrated  and  acted 
upon  by  a  strong  current.  In  a  dilute  liquid,  the  current 
being  feeble,  the  deposit  was  compact  and  metallic  in 
appearance  (free  acid  should  be  present).  From  neutral 
solutions,  although  very  dilute,  the  metal  is  separated  in 
a  flocculent  condition  by  the  feeblest  currents.  There- 
fore, to  obtain  results  that  would  answer  for  quantitative 
analysis,  the  following  conditions  were  adopted  :  The  total 
dilution  of  the  solution  was  200  c.c. ;  in  this  there  were 
0.03-0.04  gram  of  silver,  and  3-6  grams  of  free  nitric  acid. 
The  poles  were  separated  about  i  cm.  from  each  other, 
while  the  current  at  5o°-6o°  was  N.D100  =  0.04-0.05  am- 
pere, and  at  the  ordinary  temperature  it  was  N.D100  = 
o.  i -o.  2  ampere  and  2  volts. 
8 


82 


ELECTRO-CHEMICAL    ANALYSIS. 


In  the  experiments  of  Fresenius  and  Bergmann  appa- 
ratus similar  to  that  in  Fig.  34  was  employed.  It  has 
some  decided  advantages.  Both  spiral  (a)  and  cone  (b) 
are  constructed  of  platinum.  The  metallic  deposition,  it 
will  be  understood,  occurs  upon  the  cone,  the  sides  of 
which  are  perforated,  so  that  a  uniform  concentration  of 
liquid  is  preserved  throughout  the  decomposition.  When 

FIG.  34. 


liquid  electrolytes  contain  much  iron,  it  is  essential  that 
the  oxygen  liberated  within  the  cone  should  be  equally 
distributed  over  its  outer  surface.  This  is  made  possible 
through  openings.  The  shape  of  the  cone  also  prevents 
loss  from  the  bursting  of  the  bubbles  arising  from  the 
platinum  spiral  in  connection  with  the  anode. 

Krutwig  advises  adding  a  large  excess  of  ammonium 
sulphate  to  the  silver  solution,  previously  made  alkaline 
with  ammonium  hydroxide,  and  employs  a  current  of 
N.D100  =  0.02-0.05  ampere  and  2.5  volts.  In  this  way, 
o.  i  gram  of  silver  may  be  precipitated  in  two  hours. 


DETERMINATION    OF    METALS SILVER.  83 

The  writer's  experience  has  chiefly  been  with  solutions 
of  silver  containing  an  excess  of  a  pure  alkaline  cyanide. 
With  these  peroxide  separation  does  not  occur,  and  a  very 
weak  current  will  precipitate  0.15-0.20  gram  of  metal  in 
ten  hours  from  a  cold  solution.  If  the  liquid  be  heated  to 
65°  C.,  during  the  decomposition,  as  much  as  0.2-0.3  gram 
of  metal  may  be  precipitated  in  three  and  one-half  hours. 
The  current  density  for  this  precipitation  should  be  N.D100 
=  0.07  ampere.  Several  examples  from  a  student's  note- 
book will  show  how  well  the  method  works : — 


DILU-  POTASSIUM  SILVER 

SILVER.          TION.   CYANIDE.    CURRENT.  TEMPER-  TIME.        FOUND. 


GRAM. 

C.c. 

GRAMS. 

N.DIOO 

VOLTS. 

ATURE. 

HOURS. 

GRAM. 

I  . 

.0.2133 

125 

2 

0.03    A 

2-5 

65° 

4 

0.2132 

2  . 

.0.2133 

125 

2 

0.03    A 

2-5 

60° 

3 

0.2133 

3  • 

•  0.2133 

125 

4 

0.04    A 

2.5 

60° 

3 

0.2131 

4  • 

.  0.2133 

125 

2 

0.025  A 

2.7 

60° 

4 

0.2134 

5  • 

.  0.2133 

125 

2 

0.025  A 

2.7 

60° 

3 

0.2135 

6  . 

•  0.2133 

125 

2 

0.025  A 

2.7 

60° 

4 

0.2125 

In  trials  i  and  2  the  metal  was  precipitated  upon  a  dish, 
while  in  3  and  4  a  plate  cathode,  and  in  5  and  6  a  cone  was 
used  to  receive  the  silver,  which  was  very  adherent,  and 
brilliant  in  lustre.  It  was  washed  with  water,  alcohol, 
and  ether. 

Chlorine,  bromine,  and  iodine  can  be  indirectly  esti- 
mated electrolytically  by  first  precipitating  them  as  silver 
salts,  then  dissolving  the  latter  in  potassium  cyanide,  and 
exposing  the  resulting  solution  to  the  action  of  a  current 
from  three  to  four  "  Crowfoot "  cells. 

Luckow  reduced  silver  chloride  by  placing  it  in  a  plati- 
num dish,  serving  as  the  negative  electrode,  covering  it 
with  dilute  sulphuric  or  acetic  acid,  and  allowing  the  posi- 
tive electrode  to  project  into  the  solution.  Four  Meidin- 


84  ELECTRO-CHEMICAL    ANALYSIS. 

ger  cells  were  strong  enough  to  reduce  o.  i  gram  of  silver 
chloride  in  ten  minutes.  The  deposit,  while  spongy,  was 
adherent.  It  was  washed  with  water  and  then  thor- 
oughly dried  to  insure  the  absence  of  any  acid.  (See  the 
reference  to  Kinnicutt's  experiments;  also,  Prescott  and 
Dunn,  Jr.  An.  Ch.,  3,  373.) 


ZINC. 

LITERATURE. — Wrightson,  Z.  f.  a.  Ch.,  15,  303;  Parodi  and  Mascaz- 
zini,  Ber.,  10,  1098;  Z.  f.  a.  Ch.,  18.587;  Riche,  Z.  f.  a.  Ch.,  17,  216; 
Beilstein  and  Jawein,  Ber.,  12,  446;  Z.  f.  a.  Ch.,  18,  588;  Riche,  Z.  f.  a. 
Ch.,  21,  119;  Reinhardt  and  Ihle,  Jr.  f.  pkt.  Ch.  [N.  F.],  24,  193;  Clas- 
sen and  v.  Reiss,  Ber.,  14,  1622;  Gibbs,  Z.  f.  a.  Ch.,  22,  558;  Luckow, 
Z.  f.  a.  Ch.,  25,  113;  Brand,  Z.  f.  a.  Ch.,  28,  581  ;  Warwick,  Z.  f.  anorg. 
Ch.,  I,  258;  Vortmann,  Ber.,  24,  2753;  Rudorff,  Z.  f.  ang.  Ch.,  Jahrg. 
1892,  197  ;  Vortmann,  M.  f.  Ch.,  14,  536  ;  v.  Malapert,  Z.  f.  a.  Ch.,  26, 
56;  Herrick,  Jr.  An.  Ch. ,  2,  167;  Jordis,  Z.  f.  Elektrochem.,  2,  138,  563, 
655  ;  Millot,  B.  s.  Ch.  Paris,  37,  339  ;  v.  Foregger,  Dissertation,  Bern,  1896  ; 
Rider er,  J.  Arn.  Ch.  S.,  21,  789  ;  Nicholson  and  A  ver  y ,  J.  Am.  Ch.  S.,  18, 
659;  Pa  week,  Berg-Hutt.  Z.,  46,  570-573. 

Much  has  been  written  upon  the  electrolytic  estimation 
of  zinc.  The  personal  experience  of  the  writer  inclines 
him  to  give  preference  to  the  method  suggested  by  Parodi 
and  Mascazzini.  They  recommended  that  the  metal  be 
present  in  solution  as  sulphate;  its  quantity  may  vary 
from  0.1-0.25  gram.  To  it  add  4  c.c.  of  a  solution  of 
ammonium  acetate,  20  c.c.  of  citric  acid,  and  dilute  to  200 
c.c.  with  water.  The  electrodes  are  then  introduced  into 
the  liquid,  their  distance  apart  being  not  more  than  a  few 
millimetres.  The  precipitation  can  be  made  in  a  beaker 
glass,  using  a  weighed  platinum  cone  (Fig.  34)  as  the 
cathode.  The  current  for  this  purpose  should  be  0.5 
ampere  and  5.9-6.3  volts.  At  5o°-6o°,  with  a  current  of 


DETERMINATION    OF    METALS ZINC.  85 

0.5  ampere,  the  pressure  will  be  4.8-5.2  volts  and  the  de- 
posit of  metal  will  be  most  satisfactory.  When  the  pre- 
cipitation of  metal  has  ended,  which  may  be  ascertained 
by  removing  a  small  quantity  of  the  liquid  with  a  capil- 
lary tube  and  bringing  it  in  contact  with  a  drop  of  a  solu- 
tion of  potassium  ferrocyanide,  remove  the  bulk  of  the 
liquid  with  a  siphon.  Wash  the  deposit  with  water  and 
alcohol.  There  is  no  danger  of  oxidation  during  the  dry- 
ing process.  It  will  be  discovered  on  dissolving  the  pre- 
cipitated zinc  that  the  platinum  is  covered  with  a  black 
powdery  layer,  insoluble  even  in  hot  hydrochloric  or  hot 
nitric  acid.  This  is  platinum  black  (Vortmann,  Riidorff). 
It  is  exceedingly  difficult  to  remove,  and  to  prevent  its 
occurrence  it  is  best  to  coat  the  platinum  dish  with  a  thin 
layer  of  copper  or  silver  before  precipitating  the  zinc  (p. 
88). 

Beilstein  and  Jawein  add  sodium  hydroxide  to  the  solu- 
tions of  zinc  nitrate  or  sulphate,  until  a  precipitate  is  pro- 
duced, dissolve  it  in  potassium  cyanide,  and  dilute  with 
water  to  150  c.c.  The  decomposition  is  carried  out  in  a 
rather  large  beaker  glass,  the  cathode  being  either  the 
platinum  cone  already  described  (p.  82),  or  a  rather  large 
platinum  crucible  suspended  from  a  cork  (p.  61),  per- 
forated by  a  copper  wire,  touching  the  inner  surface  of  the 
crucible.  If  the  decomposition  takes  place  at  the  ordi- 
nary temperature,  use  a  current  of  N.D100  =0.5  ampere 
and  5.8  volts.  The  precipitation  will  be  complete  in  from 
two  to  two  and  one-half  hours.  It  may  be  reduced  to  one 
and  one-half  to  one  and  three-quarter  hours  by  heating 
the  electrolyte  to  60°  and  applying  a  current  of  the  density 
just  given  and  5  volts.  Wash  the  deposit  as  instructed 
above. 

Reinhardt  and   Ihle  have  objected  to  nearly  all  the 


86  ELECTRO- CHEMICAL    ANALYSIS. 

methods  which  have  been  proposed  for  the  electrolytic 
estimation  of  zinc.  They  say  of  the  Beilstein  and  Jawein 
method  ....  that  the  results  are  fairly  good, 

.  but  a  strong  current  is  necessary,  otherwise 
the  precipitation  of  the  zinc  is  slow  and  incomplete,  .... 
the  positive  pole  diminishes  in  weight  very  appreciably, 

.  finally,  working  with  potassium  cyanide  is  very 
unpleasant.  The  writer's  experience  has  proved  that  a 
current  considerably  less  than  that  which  Beilstein  and 
Jawein  first  recommended  will  throw  out  all  the  zinc  in 
the  course  of  a  night,  and  further  that  the  anode  is  not 
appreciably  affected.  The  method  suggested  by  Rein- 
hardt  and  Ihle  is,  however,  very  excellent  and  deserves 
trial  by  all  interested  in  the  electrolytic  estimation  of  zinc. 
Its  essential  features,  taken  from  their  publication,  are 
these:  Mix  the  solution  of  zinc  sulphate  or  chloride, 
neutral  as  possible,  with  an  excess  of  neutral  potassium 
oxalate,  until  the  precipitate,  which  appears  at  first,  re- 
dissolves.  Or,  observing  the  recommendation  of  Classen, 
add  4  grams  of  potassium  or  ammonium  oxalate  to  the 
solution,  acidulate  the  latter  with  tartaric  acid  (3  :  50), 
dilute  to  150  c.c.  with  water,  heat  to  60°,  and  electrolyze 
in  copper-coated  platinum  dishes  with  N.D100  =  0.5-1.5 
amperes  and  3.5-3.8  volts.  Two  hours  will  be  sufficient 
for  complete  precipitation. 

The  immediate  decomposition  of  the  zinc  oxalate  is  into 
zinc  and  carbon  dioxide  (two  molecules),  and  the  potas- 
sium oxalate  into  carbon  dioxide  (two  molecules)  and 
potassium;  the  latter  then  reacts  with  the  water,  so  that 
while  an  abundant  liberation  of  hydrogen  occurs  at  the 
cathode,  the  alkali  simultaneously  set  free  is  converted 
into  acid  potassium  carbonate  by  the  carbon  dioxide  at 
the  anode : — 


DETERMINATION    OF    METALS ZINC.  87 

ZnC2O4  -f  K2C2O4  =  (Zn  +  2KOH  -f  H2)  +  4CO2. 
Cathode.  Anode. 

2KOH  +  2CO,  = 

Therefore,  just  as  long  as  zinc  oxalate  is  being  decom- 
posed, considerable  evolution  of  gas  is  noticeable  at  the 
positive  electrode,  and  when  this  diminishes,  and  occa- 
sional bubbles  escape,  the  decomposition  is  complete,  and 
the  deposition  of  metal  may  be  considered  finished. 

Free  oxalic  acid,  or  any  other  acid,  is  not  injurious  if 
there  is  a  sufficient  quantity  of  potassium  oxalate  present. 
Nitric  acid,  however,  free  or  combined,  should  be  avoided; 
it  gives  rise  to  ammonium  salts,  which  prevent  the  zinc 
from  separating  in  a  dense  form.  The  acid  potassium 
carbonate  produced  during  the  decomposition  offers  great 
resistance  to  the  current;  it  is,  therefore,  advisable  to  add 
potassium  sulphate  to  the  solution  to  increase  its  con- 
ductivity. Reinhardt  and  Ihle  recommend  the  following 
solutions  for  use  in  decompositions  like  that  just  de- 
scribed: 1 66  grams  of  potassium  oxalate  in  i  litre  of 
water ;  250  grams  of  potassium  sulphate  in  i  litre  of  water, 
and  a  solution  of  oxalic  acid  saturated  at  15°  C. 

Experiments. — (i)  40  c.c.  of  a  solution  of  zinc  sulphate 
(=  0.181 2  gram  of  metallic  zinc),  to  which  were  added  50 
c.c.  of  potassium  oxalate  and  100  c.c.  of  potassium  sul- 
phate, were  electrolyzed  with  a  current  of  N.D100  —  0.3 
ampere  and  3.9-4.2  volts,  at  the  ordinary  temperature. 
After  three  to  four  hours  the  current  was  interrupted. 
The  precipitated  zinc  weighed  0.1814  gram.  (2)  2.1867 
grams  of  brass  (containing  tin,  copper,  lead,  and  zinc)  were 
dissolved  in  nitric  acid  and  the  tin  determined  in  the  usual 
gravimetric  way.  Its  quantity  was  found  to  be  0.04  per 
cent.  In  the  nitrate,  containing  nitric  acid,  lead  and 
copper  were  determined  simultaneously  by  electrolysis 


ELECTRO-CHEMICAL    ANALYSIS. 

(the  copper  separated  upon  the  cathode  and  the  lead  as 
dioxide  upon  the  anode) : — 

/«— 0.85%  Pb  and  64.60%  Cu. 

;"   "    "    64.62"    " 


The  acid  liquid  was  siphoned  off  from  the  deposits,  evap- 
orated to  dryness  with  sulphuric  acid,  neutralized  with 
caustic  potash,  and  then  to  this  (100  c.c.  in  volume)  solu- 
tion were  added  50  c.c.  of  a  solution  of  potassium  oxalate 
and  100  c.c.  of  a  solution  of  potassium  sulphate.  The  zinc 
found  equaled  34.50  per  cent. 

When  using  this  method  employ  a  stout  platinum  wire, 
wound  to  a  spiral  at  the  one  end,  for  the  anode,  and  a  plati- 
num cone  for  the  cathode  (p.  82).  To  avoid  the  peculiar 
spots  which  electrolytic  zinc  shows  upon  a  platinum  sur- 
face, it  will  be  best  to  first  coat  the  negative  electrode 
with  copper  (5  grams).  In  dissolving  the  precipitated 
zinc,  use  rather  dilute  nitric  acid.  The  copper  layer  will 
be  but  slightly  attacked,  and  after  washing  and  drying 
will  serve  for  further  depositions.  Wash  the  zinc  deposit 
with  water,  alcohol,  and  ether;  dry  in  a  desiccator. 
Oxidation  is  liable  to  occur  if  an  air-bath  be  used  for  the 
drying. 

Jordis  prefers  lactic  to  oxalic  acid  in  the  electrolysis  of 
zinc  salts.  To  the  solution  containing  0.2  gram  of  metal- 
lic zinc  he  added  5  grams  of  ammonium  lactate,  2  grams 
of  lactic  acid,  and  5  grams  of  ammonium  sulphate.  The 
liquid  was  diluted  to  230  c.c.  and  acted  upon  at  60°  with 
a  current  of  N.D,00  =  0.10-0.23  ampere  and  3.4-3.9  volts. 
The  electrolyte  was  usually  agitated  (p.  77).  The  anode 
and  cathode  were  1.5  cm.  apart.  The  time  for  complete 
precipitation  occupied  four  and  a  quarter  hours.  A  cop- 
per-plated platinum  dish  was  used  as  cathode. 


DETERMINATION    OF    METALS ZINC.  89 

Nicholson  and  Avery,  adopting  the  suggestion  of  War- 
wick, add  3  c.c.  of  formic  acid  to  the  zinc  salt  solution, 
then  nearly  neutralize  with  sodium  carbonate,  dilute  to 
150  c.c.,  and  electrolyze  at  the  ordinary  temperature  with 
a  current  varying  from  0.5  to  i  ampere. 

Millot,  Kiliani,  and  v.  Foregger  use  sodium  zincate  as 
electrolyte,  giving  the  following  example :  To  the  solution 
of  i  gram  of  zinc  sulphate  add  2  to  4  grams  of  sodium 
hydroxide,  dilute  to  125  c.c.  with  water,  heat  to  50°,  and 
electrolyze  with  N.D100  =  0.7-1.5  amperes  and  3.9-4.5 
volts.  All  of  the  metal  will  be  deposited  in  two  hours.  The 
character  of  the  deposit  is  improved  with  the  increase  in 
the  quantity  of  sodium  hydroxide. 

Riche  employs  "  a  solution  of  the  acetate  with  an  excess 
of  ammonium  acetate,  obtained  by  supersaturation  with 
ammonia  and  acidifying  with  acetic  acid."  This  method 
affords  good  results,  as  may  be  seen  from  the  following 
determination :  0.4736  gram  of  zinc  sulphate  was  dissolved 
in  200  c.c.  of  water,  to  which  were  added  3  grams  of 
sodium  acetate  and  10  drops  of  ordinary  acetic  acid. 
When  there  is  an  insufficiency  of  acetic  acid,  the  zinc  de- 
posit becomes  spongy.  Ammonium  acetate  may  be  sub- 
stituted for  the  sodium  salt.  After  two  hours  0.1063 
gram  of  metallic  zinc  was  obtained,  the  required  quantity 
being  0.1072*  gram.  The  temperature  should  be  60°  and 
the  current  N.Dlft0  =  0.5  ampere  and  4.8-5.2  volts. 

Moore  seems  to  have  obtained  exceedingly  satisfactory 
results  by  precipitating  a  solution  of  zinc  sulphate  with 
sodic  phosphate,  then  adding  an  excess  of  ammonium 
carbonate,  and  after  dissolving  the  precipitate  in  potas- 
sium cyanide,  the  solution  was  electrolyzed  at  a  tempera- 
ture of  80°.  (See  method  of  Beilstein  and  Jawein.)  The 
metal  was  deposited  upon  a  silver-plated  electrode.  An 


9O  ELECTRO-CHEMICAL    ANALYSIS. 

excellent  procedure,  originating  with  Luckow  and  pre- 
viously noticed  in  the  Historical  section,  consists  in  intro- 
ducing 0.5  gram  of  metallic  mercury  into  the  dish  in  which 
it  is  intended  to  electrolyze  the  solution  of  the  zinc  salt. 
It  is,  of  course,  understood  that  the  platinum  dish  and  the 
drop  of  mercury  are  weighed  together.  A  zinc  amalgam 
is  precipitated ;  it  distributes  itself  in  a  beautiful  adherent 
layer  over  the  surface  of  the  dish. 

Pa  week  believes  that  in  the  amalgam  method  suggested 
by  Vortmann  much  inconvenience  is  experienced  in 
weighing  out  the  mercuric  chloride  and  subsequently 
re-calculating  it  into  metal;  further,  that  by  frequent  use 
the  surface  of  the  platinum  cathode  changes  to  spongy 
platinum,  thus  giving  rise  to  considerable  loss.  To  avoid 
these  disadvantages  he  suggests  the  use  of  amalgamated 
zinc  or  brass  electrodes  in  gauze  form.  The  introduction 
of  these  eliminates  the  addition  of  a  mercury  salt,  while 
the  gauze  form  favors  the  deposition  and  prevents  the 
collection  of  hydrogen  bubbles  on  the  under  side  of  the 
cathode,  whereby  a  spongy  zinc  deposit  is  likely  to  be  pro- 
duced. The  gauze  electrodes  are  semi-cylindrical  in 
shape,  6  cm.  in  diameter,  two  being  attached  to  a  brass 
rod  at  a  distance  of  1 2  mm.  After  they  have  been  cleaned, 
they  are  amalgamated  or  coated  with  mercury  by  electro- 
lyzing  a  solution  containing  0.6  gram  of  mercuric  chloride. 
The  amalgam  is  washed  with  alcohol,  ether,  dried  and 
weighed.  The  electrolyte  contains  the  zinc  salt,  Seig- 
nette  salt,  and  alkali.  It  may  be  electrolyzed  with  a  cur- 
rent of  0.1-0.5  ampere  and  2.6-3.6  volts.  The  deposit 
should  be  dried  at  3O°-4O°.  (See  p.  60.) 

Vortmann  has  found  that  zinc  may  be  readily  precipi- 
tated from  its  solution  in  the  presence  of  an  excess  of 
sodium  hydroxide  and  sodium  tartrate.  The  deposit  is 


DETERMINATION    OF    METALS NICKEL,  COBALT.        9  I 

gray  in  color  and  adheres  well  to  the  dish.  The  current 
density  (N.D100)  may  vary  from  0.3-0.6  ampere.  To  de- 
termine when  the  precipitation  is  complete,  remove  a  few 
drops  of  the  liquid  and  warm  with  ammonium  sulphide. 


NICKEL  AND   COBALT. 

LITERATURE.  —  Gibbs,  Z.  f.  a.  Ch.,  3,  336;  Z.  f.  a.  Ch.,  n,  10;  22,  558; 
Merrick,  Am.  Ch.,  2,  136;  Wrightson,  Z.  f.  a.  Ch.,  15,  300,  303,  333; 
Schweder,  Z.  f.  a.  Ch.,  16,  344;  Cheney  and  Richards,  Am.  Jr.  Sc.  and 
Ar.  [3],  14,  178;  Ohl,  Z.  f.  a.  Ch.,  18,  523;  Luckow,  Z.  f.  a.  Ch.,  19,  16; 
Bergmann  and  Fresenius,  Z.  f.  a.  Ch.,  19,  314;  Riche,  Z.  f.  a.  Ch.,  21, 
116,  119;  Classen  and  v.  Reiss,  Ber.,  14,  1622,  2771;  Schucht,  Z.  f.  a. 
Ch.,  21,493;  Kohn  and  Woodgate,  Jour.  Soc.  Chem.  Industry,  8,  256; 
Riidorff,  Z.  f.  ang.  Ch  ,  Jahrg.  1892,  p.  6;  Brand,  Z.  f.  a.  Ch.,28,  588; 
Le  Roy,  C.  r.,  112,  722;  Vortmann,  M.  f.  Ch.,14,  536 ;  v.  Foregger, 
Dissertation,  1896,  Bern  ;  Campbell  and  Andrews,  J.  Am.  Ch.  S.,  17,  125; 
Oettel,  Z.  f.  Elektrochem.,  i,  192;  Fresenius  and  Bergmann,  Z.  f.  a.  Ch., 
19,  320;  Foster,  Z.  f.  Elektrochem.,  6,  160;  Winkler,  Z.  f.  anorg.  Ch., 
8,  291. 


These  metals  are  precipitated  from  solutions  of  their 
double  cyanides,  double  oxalates,  and  sulphates  mixed 
with  alkaline  acetates,  tartrates,  and  citrates,  or  from 
ammoniacal  solutions.  The  latter  seem  best  adapted  for 
nickel  depositions,  the  presence  of  ammonium  sulphate 
or  sodium  phosphate  being  favorable  to  the  precipitation. 

Fresenius  and  Bergmann,  who  have  carried  out  a  series 
of  experiments  with  nickel  and  cobalt,  give  the  following 
as  satisfactory  conditions:  50  c.c.  nickel  solution  (  = 
0.1233  gram  of  nickel),  looc.c.  of  ammonia  (sp.  gr.  0.96),  10 
c.c.  of  ammonium  sulphate  (305  grams  of  the  salt  in  i  litre 
of  water),  100  c.c.  of  water;  separation  of  the  electrodes 
J— J  cm.;  time,  four  hours.  The  current  was  N.D100  = 
0.5-0.7  ampere  and  2.8-3.3  volts  at  the  ordinary  tem- 


92 


ELECTRO-CHEMICAL    ANALYSIS. 


perature.  The  nickel  found  weighed  0.1233  gram.  Ap- 
paratus suitable  for  the  decomposition  just  described 
is  represented  in  Fig.  35.  The  metal  is  deposited  upon 
the  weighed  platinum  cone  in  the  beaker  glass,  C.  The 
vessel  is  covered  with  a  glass  lid  having  suitable  aper- 
tures for  the  positive  and  negative  electrodes.  As  soon 
as  the  blue-colored  liquid  becomes  colorless,  an  indi- 
cation that  the  metal  is  completely  precipitated,  re- 

FIG.   35. 


move  a  few  drops  and  test  with  a  solution  of  potassium 
sulphocarbonate.  If  the  latter  causes  only  a  faint  rose- 
red  coloration  the  deposition  of  metal  may  be  considered 
complete.  If  the  electrolysis  is  unnecessarily  prolonged, 
metallic  sulphide  may  be  produced  (Lehrbuch  der  analyt. 
Chemie,  Miller  and  Kiliani).  It  is  not  advisable  to  inter- 
rupt the  current  or  to  remove  the  cone  from  the  electro- 
lyzed  liquid  until  the  latter  has  been  replaced  by  water. 
This  is  effected  by  the  vessels  to  the  left  of  the  figure :  A  is 


DETERMINATION    OF    METALS NICKEL,   COBALT.        93 

an  aspirator,  filled  with  water;  B  is  air-tight  and  empty; 
x  is  a  doubly  bent  tube  extending  to  the  bottom  of  C. 
Open  p  and  the  liquid  in  C  is  gradually  transferred  to  B. 
Add  fresh  water  in  C.  Ammonium  chloride  should  not  be 
present  in  the  solution  undergoing  electrolysis. 

Vortmann  adds  tartaric  or  citric  acid  and  an  excess  of 
sodium  carbonate  to  the  solution  of  the  nickel  salt,  then 
electrolyzes  with  a  current  density  of  N.D100  =  0.3-0.4 
ampere.  The  deposit  may  contain  traces  of  carbon. 

The  statements  upon  nickel  also  apply  to  cobalt  An 
experiment,  taken  from  the  article  of  Fresenius  and  Berg- 
mann,  is  here  given  as  a  guide  in  determining  cobalt :  50 
c.c.  of  cobalt  sulphate  (=  0.1286  gram  of  cobalt),  looc.c.of 
ammonia,  loc.c.  of  ammonium  sulphate,  100 c.c.  of  water; 
current  N.D100  =  0.5-0.7  ampere  and  2.8-3.3  volts  at 
the  ordinary  temperature;  separation  of  electrodes,  J— J- 
cm.  Time,  five  hours.  The  deposited  cobalt  weighed 
0.1286  gram. 

Use  potassium  sulphocarbonate  to  test  when  the  metal 
is  fully  reduced;  it  gives  a  wine-yellow  coloration  with 
even  the  most  dilute  solutions  of  cobalt  salts. 

When  too  little  ammonia  is  present  in  the  electro- 
lyte the  results  are  bad;  too  much  of  this  reagent 
retards  the  deposition  of  the  cobalt. 

v.  Foregger  adds  15  to  20  grams  of  ammonium  car- 
bonate to  the  solution  of  i  gram  of  nickel  sulphate,  dilutes 
with  water  to  150  c.c.,  heats  to  60°,  and  electrolyzes  with 
N.D100  =  1-1.5  amperes  and  3.5-4  volts.  Two  hours 
will  be  required  for  the  precipitation. 

Oettel  observed  that  nickel  could  be,  contrary  to  gen- 
eral statements,  as  well  precipitated  from  an  ammoniacal 
chloride  as  from  an  ammoniacal  sulphate  solution.  With 
a  current  of  N.D100  =  0.45  ampere  in  the  presence  of  40 


94  ELECTRO-CHEMICAL    ANALYSIS. 

c.c.  of  free  ammonia  (sp.  gr.  0.92),  10  grams  of  ammonium 
chloride  and  nickel  chloride  equivalent  to  1.0456  grams  of 
metal,  total  dilution  200  c.c.,  he  succeeded  in  throwing 
out  1.0462  grams  of  metal  in  six  and  one-quarter  hours. 
Nitric  acid  should  not  be  present.  More  difficulty  was 
experienced  with  cobalt.  The  most  favorable  results  were 
obtained  with  a  current  of  N.D100  =  0.4-0.5  ampere. 
The  quantity  of  ammonium  chloride  should  be  at  least 
four  times  that  of  the  cobalt  and  the  solution  should  con- 
tain one-fifth  of  its  volume  of  free  ammonia  (sp.  gr.  0.92). 
When  precipitating  these  metals  from  the  solutions  of 
their  double  oxalates,  the  conditions  should  be :  4-5  grams 
of  ammonium  oxalate,  120  c.c.  total  dilution,  temperature 
6o°-7o°,  with  N.D100  =  i  ampere  and  4  volts. 

The  writer  has  electrolyzed  cobalt  compounds  contain- 
ing an  excess  of  an  alkaline  acetate  (see  Zinc)  with  per- 
fectly satisfactory  results,  and  would  recommend  such 
solutions  for  this  particular  metal. 

In  this  laboratory  the  following  conditions  are  observed 
in  precipitating  nickel  from  a  cyanide  solution:  Add  o.i 
gram  more  of  alkaline  cyanide  than  is  necessary  for  the 
precipitation  and  re-solution,  2  grams  of  ammonium  car- 
bonate, dilute  to  150  c.c.,  heat  to  60°,  and  electrolyze 
with  N.D100  =  1.5  amperes  and  6-6.5  volts.  The  nickel 
will  be  fully  precipitated  in  three  and  one-half  hours. 
Cobalt  may  be  precipitated  under  similar  conditions. 

Sodium  pyrophosphate  precipitates  a  greenish-white 
pyrophosphate  from  nickel  solutions,  an  excess  of  the 
reagent  dissolves  the  precipitate,  while  the  liquid  becomes 
yellow-green  in  color.  The  latter  is  changed  to  green  by 
ammonium  carbonate,  and  to  blue  by  ammonium  hy- 
droxide. When  electrolyzing  a  nickel  solution  add  to  it 
20  c.c.  of  a  sodium  pyrophosphate  solution,  25  c.c.  of 


DETERMINATION    OF    METALS MANGANESE.  95 

ammonia  (0.91  sp.  gr.),  and  150  c.c.  of  water.  A  current 
of  0.5  to  0.8  ampere  will  be  sufficient  to  throw  out  the 
nickel  in  nine  hours.  This  method  will  serve  equally  well 
for  the  estimation  of  cobalt. 

In  determining  nickel,  Campbell  and  Andrews  dissolve 
nickel  hydrate  in  30  c.c.  of  a  10  per  cent,  solution  of 
sodium  phosphate,  add  30  c.c.  of  ammonia  to  the  same, 
dilute  to  125  c.c.,  and  electrolyze  with  N.D100  =  0.14  am- 
pere, the  electrodes  being  separated  5  mm.  The  pre- 
cipitation is  complete  in  twelve  hours. 


MANGANESE. 

LITERATURE. — Z.  f.  a.  Ch.,  n,  14;  Riche,  Ann.  de  Chim.  et  de  Phys.  [5th 
ser.],  13,  508  ;  Lucko  w,  Z.  f.  a.  Ch.,  19,  17  ;  Schuch  t ,  Z.  f.  a.  Ch.,  22,  493  ; 
Classen  and  v.  Re  is  s,  Ber. ,  14,  1622  ;  Moore,  Ch.  News,  53,  209 ;  Smith 
and  Frank  el,  Jr.  An.  Ch.,  3,  385;  Ch.  News,  60,  262  ;  Brand,  Z.  f.  a.  Ch., 
28,  581  ;  Riidorff ,  Z.  f.  ang.  Ch.,  Jahrg.  15,  p.  6;  Classen,  Ber.,  27,  2060  ; 
Engel  s,  Z.  f.  Elektrochem.,  2,  413;  3,  286;  Groeger,  Z.  f.  ang.  Ch.  (1895), 
253;  Kaeppel,  Z.  f.  anorg.  Ch.,  16,  268. 

The  electric  current  causes  this  metal,  when  in  solution 
as  chloride,  nitrate,  or  sulphate,  to  separate  as  the  dioxide 
upon  the  anode  (see  Lead).  In  a  solution  of  nitric  acid, 
the  hydrogen  set  free  reduces  the  acid  to  oxides  of  nitro- 
gen and,  finally,  to  ammonia.  Under  such  conditions 
complications  may  arise,  particularly  if  other  metals 
are  present  in  the  solution.  For  this  reason  a  solution 
of  the  sulphate,  slightly  acidulated  with  two  to  six  drops 
of  sulphuric  acid,  is  preferable  for  electrolytic  purposes. 
Neumann  prefers  the  mineral  acid  solutions  for  these 
depositions,  and  gives  the  following  as  illustrative  ex- 
amples : 

(a)  To  the  solution  containing  0.3  gram  of  manganese 
nitrate,  add  2  c.c.  of  concentrated  nitric  acid,  dilute  to 


96  ELECTRO-CHEMICAL    ANALYSIS. 

150  c.c.  with  water,  and  electrolyze  with  N.D100  =  0.3 
ampere  and  3-3.5  volts  for  two  hours.  It  is  advisable  to 
add  the  acid  during  the  course  of  the  electrolysis.  When 
its  quantity  exceeds  3  per  cent,  the  permanganic  acid 
reaction  shows  itself. 

(b)  Add  0.5  c.c.  of  concentrated  sulphuric  acid  to  the 
solution  of  0.3  gram  of  manganese  sulphate,  dilute  to  150 
c.c.,  heat  to  6o°-7o°,  and  act  upon  the  solution  for  four 
hours  with  a  current  of  0.4-0.6  ampere  and  4  volts. 

As  soon  as  the  manganese  has  been  fully  precipitated  as 
dioxide,  the  current  is  interrupted,  the  deposit  washed 
with  water,  and  should  any  of  the  dioxide  become  de- 
tached, it  must  be  caught  upon  a  small  filter,  then  dried, 
ignited,  and  weighed,  together  with  the  adherent  dioxide, 
which  is  changed  to  protosesquioxide  (MnsO4)  before 
weighing.  Groeger  has  demonstrated  by  iodometric 
tests,  that  the  composition  of  the  precipitate  only  ap- 
proximates the  formula — MnO2.H2O — usually  assigned 
it.  Further,  it  is  useless  to  try  to  obtain  a  definite  com- 
pound by  drying.  The  product  is  so  extremely  hygro- 
scopic that  ignition  alone  to  the  protosesquioxide  will  give 
definite  and  concordant  results. 

In  the  presence  of  large  quantities  of  iron,  this  pre- 
cipitation is  unsatisfactory;  therefore,  first  remove  the 
iron  with  barium  carbonate.  Tartaric,  oxalic,  and  lactic 
acids  retard  the  formation  of  manganese  dioxide.  The 
same  is  true  of  phosphoric  acid.  Potassium  sulpho- 
cyanide  also  prevents  its  formation,  and  if  added  to  solu- 
tions in  which  dioxide  is  already  precipitated,  it  causes 
the  same  to  redissolve. 

Classen  maintains  that  strong  mineral  acids,  such  as 
nitric  and  sulphuric,  retard  the  complete  deposition  of  the 
manganese.  He  regards  acetic  acid  as  the  most  suitable 


DETERMINATION    OF    METALS MANGANESE. 


97 


of  all  the  organic  acids  for  use  in  this  precipitation.     The 
conditions  given  are :  25  c.c.  of  acetic  acid  of  specific  gravity 
1.069;   75  c-c-  °f  water;    temperature,  5o°-68°;   N.D100  = 
°-3-°-35  ampere;  V=  4.3-4.9;  time,  3  hours;  roughened 
dish. 

Engels  dissolves  the  manganese  salt  in  50  c.c.  of  water, 


FIG.  36. 


adds  10  grams  of  ammonium  acetate  and  iJ-2  grams  of 
chrome  alum,  then  dilutes  with  water  to  150  c.c.,  heats  to 
80°,  and  applies  a  current  of  N.D100  =  0.6-0.9  ampere  and 
3-4  volts.  The  deposit  is  washed  with  water  and  alcohol, 
then  dried  and  ignited.  The  deposition  was  made  in 
roughened  dishes  of  platinum.  Alcohol  (5-10  c.c.)  may  be 

9 


98  ELECTRO-CHEMICAL    ANALYSIS. 

substituted  for  the  chrome  alum,  but  more  time  will  then 
be  required  for  the  precipitation. 

Kaeppel  has  given  the  precipitation  of  manganese 
thoughtful  consideration.  He  confirms  the  experience  of 
Engels,  and  adds  that  acetone  is  a  very  desirable  addition. 
This  method  of  procedure  consists  in  heating  the  electro- 
lyte to  55°,  adding  1.5  to  10  grams  of  acetone,  and  electro- 
lyzing  with  a  current  of  N.D100  ==  0.7-1.2  amperes  and 
4-4.25  volts  for  a  period  of  from  two  to  five  hours.  The 
acetone  is  converted  into  acetic  acid,  and  it  is  the  transi- 
tional formation  of  the  latter  that  the  author  regards  as 
more  beneficial  in  the  deposition  than  if  it  be  added  di- 
rectly to  the  electrolyte. 

The  apparatus  devised  by  Herpin  (Fig.  36)  can  be  well 
applied  in  the  decomposition  of  manganese  salts.  It 
consists  of  a  platinum  dish,  A,  resting  upon  a  tripod,  B,  in 
connection  with  the  cathode  of  a  battery.  The  upper 
portion  of  the  dish  is  so  constructed  that  it  will  support 
an  inverted  glass  funnel,  D.  Any  loss  from  the  bursting 
of  bubbles  is  prevented  by  this  means.  The  anode  is  a 
platinum  spiral  C.  In  estimating  manganese  it  must  not 
be  forgotten  to  connect  the  dish  with  the  anode  of  the 
battery  employed  for  the  decomposition. 


IRON. 

LITERATURE. — Wrightson,  Z.  f.  a.  Ch.,  15,  305  ;  Parodi  and  Mascaz- 
zini,  G.  ch.  ital.,  8,  178;  also  Z.  f.  a.  Ch.,  18,  588;  Luckow,  Z.  f.  a.  Ch., 
19,  18;  Classen  and  v.  Reiss,  Ber.,  14,  1622  ;  Classen ,  Z.  f.  Elektrochem., 
i,  288  ;  Moore,  Ch.  News,  53,  209;  Smith,  Am.  Ch.  Jr.,  10,  330.  Brand, 
Z.  f.  a.  Ch.,  2#\£f  ;  Drown  and  McKenna,  Jr.  An.  Ch.,  5,  627  ;  Smith 
and  Muhr,/fr.  An.  Ch.,  5,  488;  Rudorff,  Z.  f.  ang.  Ch.,15-  Jahrg.,  p.  198  ; 
Vortmaryi,  M.  f.  Ch.,  14,  536  ;  Heidenreich,  Ber.,  29,  1585  ;  Avery  and 
Dalesx"Ber.,  32,  64,  2233  ;  Verwer  and  Groll,  Ber.,  32,  37,  806;  Goecke, 
Dissertation,  Bonn,  1900;  Kollock,  J.  Am.  Ch.  S.,  21,  928. 


DETERMINATION    OF    METALS IRON.  99 

In  the  historical  sketch  (p.  54)  it  was  mentioned  that 
Parodi  and  Mascazzini  found  that  iron  could  be  precipi- 
tated from  solutions  of  its  double  oxalates.  This  sugges- 
tion has  since  been  elaborated  by  Classen,  and  by  him 
applied  to  many  other  metals.  Following  the  recom- 
mendation of  this  chemist,  about  six  to  seven  grams  of 
ammonium  oxalate  are  dissolved  in  as  little  water  as  possi- 
ble, and  the  iron  salt  solution  gradually  added  to  it  with 
constant  stirring.  The  liquid  is  then  diluted  with  water 
to  150-175  c.c.,  and  electrolyzed  at  the  ordinary  tempera- 
ture with  a  current  of  N.D1()0  =  :  1.5  amperes  and  2-4.5 
volts,  or  at  the  temperature  of  4o°-65°  with  0.5-1.0  am- 
pere and  2-3.5  volts.  If  ferric  hydroxide  should  separate 
during  the  electrolytic  decomposition,  it  can  be  redis- 
solved  by  adding  oxalic  acid  drop  by  drop.  Test  the 
clear  liquid,  acidulated  with  hydrochloric  acid,  with 
potassium  sulphocyanide.  The  deposited  iron  has  a 
steel-gray  color;  it  should  be  washed  with  water,  alcohol, 
and  ether.  Avoid  the  presence  of  chlorides  and  nitrates. 
By  carefully  complying  with  the  conditions  recommended 
by  Classen  good  results  are  sure  to  follow.  To  show  that 
persons  with  but  little  experience  can  obtain  satisfactory 
results  with  the  preceding  method  the  two  following  de- 
terminations, made  by  a  student,  are  given :  A  quantity  of 
ferric  ammonium  sulphate  (=  0.0814  gram  of  iron)  was 
dissolved  in  200  c.c.  of  water,  and  to  this  were  added  8 
grams  of  ammonium  oxalate.  The  solution  was  heated  to 
80°,  and  in  two  hours,  with  a  current  of  1.5  amperes, 
0.0814  gram  of  iron  was  obtained.  In  a  second  experi- 
ment the  quantity  of  iron  was  doubled  (^^fo.  1628  gram 
of  iron),  while  the  ammonium  oxalate  was  n  grams,  tem- 
perature 66°,  and  the  current  i  ampere.  The  precipitated 
iron  weighed  0.1619  gram  instead  of  0.1628. 


IOO  ELECTRO-CHEMICAL    ANALYSIS. 

The  writer  found  the  following  procedure  admirably 
suited  for  iron  determinations:  10  c.c.  iron  solution  (= 
0.1277  gram  of  metal),  loc.c.  sodium  citrate  (1.8  grams) 
with  3  c.c.  of  citric  acid  (0.059  gram)>  then  diluted  with 
water  to  250  c.c.,  and  electrolyzed  with  a  current  of  N.D100 
=  0.8  ampere  and  7-8  volts  at  50°  for  four  and  one-half 
hours.  The  iron  deposit  weighed  0.1280  gram.  It  con- 
tained 0.94  per  cent,  of  carbon.  The  deposit  was  washed 
as  already  directed.  In  several  determinations  alumin- 
ium and  titanium  were  present  with  the  iron,  but  the 
latter  was  precipitated  free  from  the  other  two.  For  this 
reason  the  writer  regards  the  method  as  useful.  B.  F. 
Kern,  working  in  this  laboratory  with  the  view  of  arriving 
at  some  knowledge  in  regard  to  the  carbon  deposition, 
after  long  and  painstaking  experimentation,  recommends 
the  following  conditions  as  favorable  for  the  getting  of 
iron  deposits  free  from  the  carbon  impurity :  Add  i  gram 
of  sodium  citrate  and  o.  i  gram  of  citric  acid  to  the  solution 
of  iron  sulphate  (o.  i  gram  of  metal),  dilute  to  150  c.c.,  heat 
to  60°,  and  electrolyze  with  N.D100  =  0.8-1.3  amperes  and 
9  volts.  Just  as  soon  as  the  iron  is  precipitated,  siphon 
off  the  liquid  and  wash  without  interruption  of  the  cur- 
rent. The  opinion  exists  that  prolonged  action  of  the 
current  after  the  metal  is  all  deposited  tends  to  increase 
the  carbon  content  of  the  iron. 

From  ammoniacal  tartrate  solutions  iron  is  also  pre- 
cipitated, but  carries  carbon  with  it.  It  would  therefore 
not  be  advisable  to  use  this  electrolyte  except  in  cases 
where  separations  were  desired,  which  were  possible 
only  in  solutions  of  this  character. 

A  third  method,  originated  by  Moore,  advises  that 
glacial  phosphoric  acid  (15  per  cent,  acid)  be  added  to  the 
distinctly  acid  solution  of  ferric  chloride  or  sulphate, 


DETERMINATION    OF    METALS IRON.  IOI 

until  the  yellow  color  fully  disappears,  then  a  large  excess 
of  ammonium  carbonate  is  added  and  a  gentle  heat  is  ap- 
plied until  the  liquid  becomes  clear.  On  electrolyzing  the 
hot  (70°)  solution  with  a  current  of  2  amperes,  the  iron  is 
rapidly  and  completely  deposited  at  the  rate  of  0.75  gram 
per  hour.  Avery  and  Dales,  on  the  other  hand,  claim 
that  with  a  current  of  N.D100  =  2  amperes  and  5  volts  they 
were  not  able  to  precipitate  more  than  0.2  gram  of  iron  in 
five  hours.  The  end  of  the  decomposition  is  recognized 
by  testing  a  portion  of  the  solution  with  ammonium  sul- 
phide. Wash  the  deposit  as  already  directed. 

Recently,  quite  a  little  discussion  has  been  had  upon 
the  deposition  of  iron  and  its  enclosures.  Avery  and 
Dales  question  whether  the  metal  is  fully  precipitated 
from  any  one  of  the  electrolytes  described  in  the  preceding 
paragraphs;  furthermore,  they  affirm  that  even  from  an 
oxalate  solution  the  iron  carries  down  carbon  with  it ;  that 
oxalic  acid  is  converted  in  part,  at  least,  into  glycollic 
acid,  and  that  iron  salts  in  the  presence  of  the  latter  acid 
yield  upon  electrolysis  a  metal  strongly  contaminated 
with  hydrocarbons.  As  to  Moore's  method,  they  assert 
that  phosphorus  is  always  present  in  the  deposit  of  iron. 
Goecke  concurs  with  these  chemists  in  their  views  on  the 
cathodic  contaminations.  Verwer  and  Groll  think  that 
iron,  from  an  oxalate  solution,  is  absolutely  free  from 
carbon,  while  Classen  attributes  the  trifling  amounts  of 
carbon,  which  have  been  observed,  to  carelessness  and 
inexperience  in  the  execution  of  the  prescribed  directions. 

Drown,  pursuing  a  suggestion  made  by  Wolcott  Gibbs 
in  1883  relative  to  the  precipitation  of  metals  in  the  form 
of  amalgams,  has  applied  it  to  the  determination  of  iron. 
The  trial  tests  were  made  with  a  solution  of  ferrous  ammo- 
nium sulphate,  slightly  acidulated  with  sulphuric  acid,  to 


IO2  ELECTRO-CHEMICAL    ANALYSIS. 

which  a  large  excess  of  mercury  was  added  (not  less  than 
fifty  times  the  weight  of  the  iron  to  be  precipitated).  A 
large  platinum  anode  was  used,  while  the  mercury  cathode 
was  brought  into  the  circuit  by  means  of  a  platinum  wire 
enclosed  and  fused  into  one  end  of  a  glass  tube  which  passed 
through  the  liquid.  The  current  employed  for  the  pre- 
cipitation equaled  about  2  amperes  per  minute.  The 
author  remarks  that  if  these  conditions  be  observed,  as 
much  as  10  grams  of  iron  can  be  precipitated  in  from  ten 
to  fifteen  hours. 

The  decomposition  was  carried  out  in  beaker  glasses. 
Care  should  be  exercised  in  drying,  so  that  no  mercury  is 
volatilized. 


URANIUM. 

LITERATURE.  — Luckow,  Z.  f.  a.  Ch.,  19,  18 ;  Smith,  Am.  Ch.  Jr.,  i,  329 ; 
Smith  and  Wallace,  J.  Am.  Ch.  S.,  20,  279 ;  Kollock  and  Smith,  J.  Am. 
Ch.  S.,  23,  607;  Kern,  J.  Am.  Ch.  S.,  23,  685. 


For  electrolytic  purposes  use  the  acetate,  the  sulphate, 
or  the  nitrate.  Connect  the  dish  in  which  the  deposition 
is  made  with  the  negative  electrode  of  the  battery.  The 
uranium  separates  as  yellow  uranic  hydroxide  upon  the 
cathode;  by  the  continued  action  of  the  current  it  changes 
to  the  black  hydrated  protosesquioxide.  As  soon  as  the 
solution  becomes  colorless,  interrupt  the  current,  wash 
with  a  little  acetic  acid  and  boiling  water ;  dry,  ignite,  and 
weigh  as  protosesquioxide.  If  any  of  the  hydrate  be- 
comes detached,  collect  the  same  upon  a  small  filter,  and 
ignite  the  latter  together  with  the  dish  contents.  Con- 
ditions leading  to  successful  results  are  contained  in 
the  following  examples : — 


DETERMINATION    OF    METALS URANIUM. 


I03 


ELECTROLYSIS  OF  URANIUM  ACETATE. 


c 

a  3 


PL,  05 

o 


0.0986 
0.0986 

0.1972 

0.2298 
0.2298 


0.2 
0.2 
0.2 
O.I 
0.2 


125 
125 
125 
125 
125 


N.D107  ,zo.29  A 
N.D107^o.3  A 
N.D107=o.3  A 
N.D107  -^0.09  A 
N.D]07  =  0.07  A 


16.25 

12.2 

10-75 

4.25 
4.25 


W  o 

h 


70 

70 

70 
70 

70 


z 

S 

Q" 

K 

z 

O 

D    . 
O  en 

Z 

d* 

O 

D 

W 

0.0988 

-]  0.0002 

0.0989 

+0.0003 

0.1970 

0.0002 

0.2297 

—0.000  1 

0.2299 

+0.0001 

ELECTROLYSIS   OF    URANYL   NITRATE  SOLUTIONS. 


Ur308 
PRESENT, 
IN  GRAMS. 


DILU- 
TION. 
C.c. 


O.I222     125 
O.I222     125 


TEMPER- 
ATURE. 
°C. 

CURRENT. 

VOLTS. 

TIME. 
HOURS. 

Ur308 

FOUND,  IN 
GRAMS. 

75 

N.D107  =  0.035  A 

4.6 

51 

0.1225 

65 

N.D107  =  o.04    A 

2.25 

71 

O.  I2l8 

Quantitative  results  were  also  obtained  by  the  electrol- 
ysis of  the  sulphate.  The  neutral  salt  solution  was 
diluted  to  125  c.c.  and  heated  to  75°  C.,  when  a  current  of 
from  0.02  to  0.04  ampere  for  107  sq.  cm.  of  cathode  surface 
and  2.25  volts  was  conducted  through  the  liquid. 

ELECTROLYSIS   OF  URANYL   SULPHATE. 


z 

w" 

f- 

o 

^ 

g 

z 

w 

CJ 

« 

a 

Q" 

< 

a 
h 

0 

O 

«  « 

z 

0 

^ 

ffi 

o  w 

z 

oo(J 

H 

u 

a.    . 

a 

w 

^^ 

CK 

o 

9,z 

J 

su 

MO 

j 
o 

s 

D 

Q 

H 

U 

H 

D 

W 

0.1320 

125 

75 

N.D107  =  =0.02    A 

2 

6: 

0.1320 

0.1320 

125 

75 

N.D107  =  o.o2    A 

2 

5! 

0.1322 

-(-O.OOO2 

0.1393 

125 

75 

N.D107  =  o.o4    A 

2.25 

5 

0.1395 

-(-O.OOO2 

0-1393 

125 

70 

N.D107=  0.038  A 

2.25 

7 

0.1392 

—  O.OOOI 

IO4  ELECTRO-CHEMICAL    ANALYSIS. 

This  method  affords  an  excellent  separation  of  uranium 
from  the  alkali  and  alkaline  earth  metals  (p.  191). 


THALLIUM. 

LITERATURE. — Schucht,  Z.  f.  a.  Ch.,  22,  241,  490;  Neumann,  Ber.,  21, 
356. 

This  metal  separates  as  sesquioxide,  from  acid  solutions, 
upon  the  anode,  while  from  ammoniacal  liquids  it  is  de- 
posited partly  as  metal  and  partly  as  oxide.  From  oxa- 
late  solutions  and  from  its  double  cyanides  it  separates 
only  as  metal  when  the  current  is  feeble.  However,  diffi- 
culty is  experienced  in  drying  the  deposit  without  having 
it  oxidized.  In  this  respect  it  is  even  more  troublesome 
than  lead.  Neumann  utilizes  the  current  to  separate 
the  metal,  dissolves  the  latter  in  acid,  and  measures  the 
liberated  hydrogen;  from  its  volume  he  calculates  the 
quantity  of  thallium  originally  present.  For  suitable 
apparatus  to  carry  out  this  method  consult  the  literature 
cited  above. 

PLATINUM. 

LITERATURE. — Luckow,  Z.  f.  a.  Ch.,  19,  13;  Classen,  Ber.,  17,  2467; 
Smith,  Am.  Ch.  Jr.,  13,  206;  Rudorff,  Z.  f.  ang.  Ch.,  1892,  696. 

The  solutions  of  platinum  salts,  slightly  acidulated  with 
sulphuric  acid,  and  acted  upon  by  a  feeble  current,  give 
up  the  metal  as  a  bright,  dense  deposit  upon  the  dish, 
frequently  so  light  as  to  be  scarcely  distinguished  from 
the  latter.  In  using  platinum  vessels  for  this  purpose* 
first  coat  them  with  a  rather  thick  layer  of  copper,  upon 
which  afterward  deposit  the  metal.  Wash  the  deposit 
with  water  and  alcohol. 


DETERMINATION    OF    METALS PLATINUM.  105 

In  ordinary  gravimetric  analysis,  potassium  is  fre- 
quently estimated  as  potassio-platinum  chloride,  K2PtCl0. 
This  operation  requires  time  and  care.  Rather  dissolve 
the  double  salt  in  water,  slightly  acidulate  the  solution 
with  sulphuric  acid  (2  to  3  per  cent,  by  volume),  and 
electrolyze  with  a  current  of  N.D100  =  0.1-0.2  ampere. 
The  deposit  will  be  spongy.  On  heating  to  6o°-65°  and 
electrolyzing  with  N.D100  =  0.05  ampere  and  1.2  volts, 
the  platinum  will  be  completely  precipitated  in  from 
four  to  five  hours  in  a  perfectly  adherent  form.  It  is 
often  so  dense  as  to  be  distinguished  from  hammered 
platinum  with  difficulty. 

In  the  Munich  laboratory  the  platinum  salt  solution  is 
mixed  with  2  per  cent,  (by  volume)  of  a  dilute  sulphuric 
acid  (i  15),  heated  to  70°,  and  electrolyzed  with  N.D100  = 
0.01-0.03  ampere.     The  precipitation  will  be  complete  in 
five  hours. 

The  following  experiment  executed  in  this  laboratory 
demonstrates  that  the  precipitation  of  platinum  from 
solutions  containing  sodium  phosphate  and  free  phos- 
phoric acid  is  complete.  The  volume  of  the  liquid  was 
150  c.c.  It  contained  0.1144  gram  of  metallic  platinum, 
30  c.c.  of  disodium  hydrogen  phosphate  (sp.  gr.  1.0358), 
and  5  c.c.  of  phosphoric  acid  (sp.  gr.  1.347).  The  cur~ 
rent  equaled  0.8  ampere.  The  deposit  of  platinum 
weighed  0.1140  gram.  It  was  precipitated  upon  a  cop- 
per-coated platinum  dish.  It  was  washed  with  water 
and  alcohol.  Ten  hours  were  required  for  the  deposition. 


10 


IO6  ELECTRO-CHEMICAL   ANALYSIS. 


PALLADIUM. 

LITERATURE. — Wohler,  Ann.,  143,  375;  Schucht,  Z.  f.  a.  Ch.,  22,  242; 
Smith  and  Keller,  Am.  Ch.  Jr.,  12,  252  ;  Smith,  Am.  Ch.  Jr.,  13,  206  ;  14, 
435  >  J°ly  and  Leidie,  C.  r.,  116,  146  ;  Z.  f.  anorg.  Ch.,  3,  476. 

Palladium  can  be  deposited  from  solutions  of  the  same 
kind  and  in  the  same  manner  as  platinum.  A  bright 
metallic  deposit  will  be  obtained  by  the  use  of  a  current 
of  N.D100  =  0.05  ampere  and  1.2  volts;  otherwise  it  is 
spongy. 

It  has  been  discovered,  in  this  laboratory,  that  this 
metal  can  be  rapidly  and  fully  precipitated  from  ammoni- 
acal  solutions  of  palladammonium  chloride,  Pd(NH3Cl)2, 
which  may  be  prepared  by  adding  hydrochloric  acid  to  an 
ammonium  hydroxide  solution  of  palladious  chloride. 
To  show  the  accuracy  of  this  method,  several  actual  de- 
terminations are  here  introduced:  (i)  A  quantity  of  the 
double  salt  (=  0.2228  gram  of  palladium)  was  dissolved  in 
ammonium  hydroxide;  to  this  solution  were  added  20-30 
c.c.  of  the  same  reagent  (sp.  gr.  0.935)  and  100  c.c.  of 
water.  A  current  of  0.07-0.1  ampere  acted  upon  this 
mixture  through  the  night,  and  deposited  0.2225  gram  of 
palladium.  (2)  In  another  experiment,  with  conditions 
similar  to  those  just  mentioned,  excepting  that  the  quan- 
tity of  the  palladammonium  chloride  was  doubled,  and 
the  current  held  at  0.7  ampere,  the  quantity  of  metal 
precipitated  equaled  0.4462  gram  instead  of  0.4456. 
Oxide  did  not  separate  upon  the  anode.  The  deposit, 
when  dry,  showed  the  same  appearance  as  is  ordinarily 
observed  with  this  metal  in  sheet  form.  It  was  washed 
with  hot  (70°)  water,  and  dried  in  an  air-bath  at  no°- 
115°.  It  is  best  to  deposit  the  palladium  in  platinum 
dishes  previously  coated  with  silver. 


DETERMINATION    OF    METALS RHODIUM.  1 07 


RHODIUM. 

LITERATURE. — Smith,  Jr.  An.  Ch.,  5,  201;    Joly  and    Leidie,    C.    r., 
2,  793- 


Few  attempts  have  been  made  to  determine  this  metal 
electrolytically.  Its  separation  from  an  acid  phosphate 
solution  is  very  rapid  and  complete.  A  current  of  o.  18 
ampere  will  answer  perfectly  for  the  purpose.  As  the 
decomposition  progresses,  the  beautiful  purple  color 
of  the  liquid  gradually  disappears,  and  the  solution  is 
colorless  when  the  precipitation  is  finished.  The  depo- 
sition of  the  rhodium  should  be  made  upon  copper-coated 
dishes.  The  metal  is  generally  black  in  color,  very  com- 
pact, and  perfectly  adherent.  Hot  water  may  be  used 
for  washing  purposes. 

Joly  precipitates  the  metal  from  solutions  acidulated 
with  sulphuric  acid. 


MOLYBDENUM. 

LITERATURE. — Smith,  Am.  Ch.  Jr.,   I,  329;   Hoskinson   and   Smith, 
ibid.,  7,  90;   Kollock  and  Smith,  J.  Am.  Ch.  S.,  23,  669. 


When  the  electric  current  acts  upon  ammoniacal  or 
feebly  acid  solutions  of  ammonium  molybdate,  a  beautiful 
iridescence  appears;  as  the  action  continues  this  assumes 
a  black  color,  and  the  deposit  becomes  more  dense.  It  is 
the  hydrated  sesquioxide  which  is  precipitated.  At  the 
time  when  these  observations  were  made,  experiments 
were  instituted  to  determine  the  metal.  The  results, 
while  quantitative  in  character,  were  obtained  with  the 


IO8  ELECTRO-CHEMICAL    ANALYSIS. 

consumption  of  too  much  time  to  permit  of  the  method 
being  generally  applied.  Recently  attention  has  again 
been  given  to  the  subject  in  this  laboratory.  Sodium 
molybdate  (Na2MoO4.2H2O)  was  dissolved  so  that  0.1302 
gram  of  molybdenum  trioxide  was  present  in  125  c.c.  of 
solution,  which  was  exposed  for  several  hours  to  the  action 
of  a  current  of  o.  i  ampere  and  4  volts.  The  temperature 
of  the  electrolyte  was  75°  C.  No  precipitation  occurred 
upon  either  electrode.  Upon  adding  two  drops  of  con- 
centrated sulphuric  acid  to  the  liquid,  it  at  once  assumed 
a  dark  blue  color.  As  the  current  continued  to  act, 
this  color  disappeared  and  the  cathode  was  coated  with  a 
black  deposit — the  hydrated  sesquioxide.  On  removing 
the  colorless  liquid  and  testing  it  with  ammonium  thio- 
cyanide,  zinc,  and  hydrochloric  acid,  evidences  of  the 
presence  of  molybdenum  failed  to  appear.  The  deposit 
was  brilliant  black  in  color  and  so  adherent  that  it  could 
be  washed  without  detaching  any  particles.  Usually  the 
colorless  liquid  was  removed  with  a  siphon,  cold  water 
being  introduced  without  interrupting  the  current.  The 
deposit  was  not  dried,  but  dissolved  while  moist  from  off 
the  dish  in  dilute  nitric  acid,  and  the  solution  carefully 
evaporated  to  dryness,  the  residue  being  heated  upon  an 
iron  plate  to  expel  the  final  traces  of  acid.  White  molyb- 
dic  acid  remained.  If  blue  spots  appeared  in  the  mass, 
they  were  removed  by  moistening  the  residue  with  nitric 
acid  and  evaporating  a  second  time  to  dryness.  This 
procedure  was  adopted  in  all  the  experiments.  It  was 
not  possible  to  obtain  concordant  results  by  merely  drying 
the  hydrate  at  a  definite  temperature.  The  same  was 
true  in  regard  to  the  ignition  of  the  hydrate  to  trioxide. 
L/oss  occurred  from  sublimation  and  volatilization. 


DETERMINATION    OF    METALS  -  MOLYBDENUM. 
RESULTS. 


IOQ 


S      z 

U 

w 

5  w  " 

U  UJ 

U 

§ 

a2Hg 

Q  X  Z  | 

D°U 

Z 

^u 

U 

S 

«  o  a  z 

>.   «  (fl  ^ 

£   u 

u° 

0 

2  a:  wo 

£j 

£> 

oh* 

(J)  ^ 

J 

s 

a 

U 

p 

H 

0.1302 

O.I 

12^ 

70 

N.D107  =  0.022  A 

2.O 

0.1302 

O.I 

125 

80 

N.D107  =  0.045  A 

2.2S 

0.1302 

O.I 

125 

70 

N.D107^o.o4    A 

2.2 

0.2604 

O.  2 

125 

7S 

N.D107=o.o4    A 

2.O 

0.1541 

O.2 

125 

85 

N.D107  =  o.04    A 

1.9 

0.1541 

O.  2 

I25 

80 

N.D]07  =  0.035  A 

2.1 

§2"  w 

Q  X  Q  S 
M  0  Z  < 

0  < 
u  x 

|Hg 

W 

o.  1299     —  0.0003 

0.1302 

.    .     . 

0.1302 
0.2603 

—  O.OOOI 

0.1541 
0.1540 

—  O.OOOI 

The  method  is  accurate,  is  easy  of  execution,  and  re- 
quires comparatively  little  time. 

It  seemed  that  the  method  could  be  made  useful  in  the 
determination  of  the  molybdenum  content  of  the  mineral 
molybdenite.  By  fusing  the  latter  with  a  mixture  of  pure 
alkaline  carbonate  and  nitrate,  sodium  molybdate  and 
sulphate  would  be  formed.  If  the  sulphur  is  not  to  be 
determined,  after  dissolving  out  the  fusion  with  water,  and 
filtering  off  the  insoluble  oxides,  acidulate  the  alkaline 
liquid  with  dilute  sulphuric  acid  and  proceed  with  the 
electrolysis;  but  in  cases  where  an  estimation  of  the  sul- 
phur is  desired,  it  was  thought  that  acetic  acid  would 
answer  for  the  purpose  of  acidulation.  To  ascertain  the 
latter  fact  the  experiments  given  below  were  instituted. 
The  solution,  acidified  with  this  acid,  does  not  acquire  a 
blue  color  on  passing  the  current  through  it.  The  deposit 
of  hydrated  oxide  is  very  adherent  and  readily  washed. 
A  longer  time  is  necessary  for  the  complete  precipitation. 
It  is  also  advisable  not  to  add  the  entire  volume  of  acetic 
acid  at  first,  but  to  introduce  it  gradually  from  time  to 
time,  from  a  burette. 


10 


ELECTRO-CHEMICAL    ANALYSIS. 


RESULTS. 


i 

§     z 

h  D  cj 

u 

a 

W 

§ 

sg"  . 

a  «  H  w 

u  5u 

U 

H 

z 

M 

§ 

^Q  "  CA 

2 

"  w 

2' 

<  ^  ? 

a 

h 

T 

O  X  Q"  S 

of  2 

*  2  $  ^ 

w  H  § 

a° 

M 

0 

§  2Z  ^ 

§2 

""'  *•    w  o 

pu   W   Q 

D 

^ 

a 

•^  ^  o  O 

So 

Q  r*  ai 

^  Q 

J 

u 

^ 

Q  £—  '  N. 

w 

g>« 

Q 

r1 

H 

s 

0.1541 

i 

125 

85   ;N.D107=:o.o75A 

4-4 

71 

0.1541 

0.1541 

i 

125 

85      N.D107  =  0.075  A 

4-4 

3 

0.1540 

—  O.OOOI 

0.1541 

i 

I25 

80     N.D10.  =0.05    A 

2-5 

6 

0.1543 

-f-  O.OOO2 

In  the  last  experiment,  5  grams  of  sodium  acetate  were 
added  in  order  to  increase  the  conductivity  of  the  solution 
and  to  ascertain  what  effect  an  excess  of  this  salt  would 
have,  because,  if  the  acetic  acid  were  used  to  acidify  the 
alkaline  solution  obtained  by  the  decomposition  of  molyb- 
denite, a  great  deal  of  this  salt  would  be  present.  The 
concordant  results  justified  the  next  step,  which  was  to 
decompose  weighed  amounts  of  pulverized  molybdenite 
with  sodium  carbonate  and  nitrate,  then  take  up  the 
fusion  with  water,  filter  out  the  insoluble  oxides,  acidify 
with  acetic  acid,  boil  off  the  carbon  dioxide,  and  electro- 
lyze.  The  liquid  poured  off  from  the  deposit  of  the  ses- 
quihydroxide  was  heated  to  boiling  and  precipitated  with 
a  hot  solution  of  barium  chloride. 


MOLYBDENITE, 
IN  GRAMS. 

I 0.2869 

2 0.1005 

3 0.1388 


MOLYBDENUM 
FOUND,  IN 
PER  CENT. 

57-37 
57.15 
56.83 


SULPHUR 
FOUND,  IN 
PER  CENT. 

38.28 
38.33 
'37.87 


DETERMINATION    OF    METALS GOLD.  I  I  I 


GOLD. 

LITERATURE. — Luckow,  Z.  f.  a.  Ch.,  ig,  14;  Brugnatelli,  Phil.  Mag., 
21,  187;  Smith,  Am.  Ch.  Jr.,  13,  206;  Smith  and  Muhr,  Am.  Ch.  Jr.,  13,  417; 
Smith,  Jr.  An.  Ch.,  5,  204;  Smith  and  Wallace,  Ber.,  25,  779;  Frankel, 
Jr.  Fr.  Ins.,  1891  ;  Persoz,  Ann.  Chim.  Pharm.,  65,  164;  Rudorff,  Z.  f. 
ang.  Ch.,  1892,  p.  695. 

This  metal  can  be  completely  deposited  from  solutions 
containing  it  in  the  form  of  a  double  cyanide,  sulphaurate, 
and  sulphocyanide,  as  well  as  in  the  presence  of  free  phos- 
phoric acid.  In  this  laboratory  the  cyanide  and  sul- 
phaurate have  received  the  most  consideration.  An 
example  will  illustrate  the  conditions  with  which  good 
results  may  be  obtained  from  the  double  cyanide :  A  solu- 
tion contained  0.1162  gram  of  metallic  gold;  to  it  were 
added  1.5  grams  of  potassium  cyanide  and  150  c.c.  of 
water.  It  was  heated  to  55°  and  electrolyzed  with  a  cur- 
rent of  N.D100  =  0.38  ampere  and  2.7-3.8  volts.  The 
precipitation  was  complete  in  one  and  one-half  hours. 
The  gold  deposit  weighed  0.1163  gram.  It  was  washed 
both  with  cold  and  hot  water.  The  metal  may  be  pre- 
cipitated upon  silver-coated  or  copper-coated  platinum 
vessels,  or  directly  upon  the  sides  of  the  platinum  dish. 
If  the  last  suggestion  is  followed,  dissolve  off  the  gold, 
after  weighing,  by  introducing  very  dilute  potassium 
cyanide  into  the  dish,  and  then  connect  the  latter  with 
the  anode  of  a  battery  yielding  a  very  feeble  current. 

The  deposition  of  gold  from  a  sodium  sulphide  solution 
(sp.  gr.  1. 1 8)  is  just  as  satisfactory  as  that  described  in  the 
last  paragraph.  The  current  should  equal  o.  1-0.2  ampere 
for  a  total  dilution  of  about  125  c.c.  The  precipitated 
metal  is  very  adherent  and  of  a  bright  yellow  color. 

The  facts  relating  to  the  electrolytic  behavior  of  vana- 


I  I  2  ELECTRO-CHEMICAL    ANALYSIS. 

dium  (Truchot,  Ann.  Chim.  Anal.  (1902),  7,  165-167), 
tungsten,  and  osmium  are,  at  the  present  writing,  few  in 
number  and  will  not  be  given  here. 


TIN. 

LITERATURE. — Luckow,  Z.  .  a.  Ch.,  19,  13;  Classen  and  v.  Reiss, 
Ber.,  14,  1622;  Gibbs,  Ch.  News,  42,  291  ;  Classen,  Ber..  17,2467;  18, 
1104;  Bongartz  and  Classen,  Ber.,  21,  2900;  Rudorff,  Z.  f.  ang.  Ch., 
1892,  199;  Classen,  Ber.,  27,  2060;  Engels,Z.  f.  Elektrochem.,  2,  418 ; 
Freudenberg,  Z.  f.  ph.  Ch.,  12,  121;  Heidenreich,  Ber.,  28,  1586; 
Campbell  and  Champion,  J.  Am.  Ch.  S.,  20,  687;  Klapproth,  Dis- 
sertation, Hannover,  1901;  Classen,  Z.  f.  Elektrochem.,  1,289. 

Tin  may  be  deposited  from  a  solution  of  ammonium  tin 
oxalate.  It  is  advisable  not  to  use  potassium  oxalate  in 
the  electrolysis,  for  then  a  basic  salt  is  liable  to  separate 
upon  the  anode. 

Classen  adds  120  c.c.  of  a  saturated  ammonium  oxalate 
solution  to  the  liquid  containing  0.9-1.0  gram  of  stannic 
ammonium  chloride,  then  electrolyzes  at  3O°-35°  with  a 
current  of  0.3-0.6  ampere  and  2.8-3.8  volts.  Acid  am- 
monium oxalate  must  be  added  from  time  to  time  if  large 
quantities  of  metal  are  to  be  precipitated.  The  tin  sepa- 
rates in  a  brilliant,  white,  adherent  form.  It  is  washed 
and  dried  in  the  usual  way.  The  time  required  for  pre- 
cipitation is  generally  nine  hours.  This  factor,  however, 
can  be  reduced,  as  is  evident  from  the  following  example : 
Acidulate  the  solution  containing  0.4  gram  of  tin  and  4 
grams  of  ammonium  oxalate  with  9-10  grams  of  oxalic 
acid;  heat  to  6o°-65°,  and  electrolyze  with  N.D100  =  1-1.5 
amperes.  Acetic  acid  may  replace  the  oxalic  acid. 
Fusion  with  potassium  acid  sulphate  will  remove  the  tin 
from  the  dish. 


DETERMINATION    OF    METALS TIN.  I  I  3 

Campbell  and  Champion  use  the  oxalate  method  in 
determining  tin  in  its  ores.  Fuse  i  gram  of  the  ore  with 
5-6  grams  of  a  mixture  of  equal  parts  of  soda  and  sulphur 
for  an  hour  and  a  half,  at  full  red  heat.  This  is  done  in  a 
porcelain  crucible,  placed  within  a  second  crucible  of  the 
same  material.  Dissolve  the  sulphostannate  in  from  40- 
50  c.c.  of  hot  water,  filter,  and  re-fuse  the  residue  as  be- 
fore. Add  hydrochloric  acid,  to  faint  acid  reaction,  to 
the  combined  solutions  of  sulpho-salts.  Stannic  sulphide 
will  be  precipitated.  Boil  off  the  hydrogen  sulphide,  add 
10  c.c.  of  hydrochloric  acid  (sp.  gr.  1.20),  and  then  gradu- 
ally introduce  2-3  grams  of  sodium  peroxide  until  a  clear 
liquid  is  obtained.  Boil  for  three  minutes,  filter  out  the 
separated  sulphur,  add  ammonia  water  to  permanent 
precipitation  and  50  c.c.  of  a  10  per  cent,  acid  ammonium 
oxalate  solution.  Electrolyze  with  a  current  of  N.D100  = 
o.  i  ampere  and  4  volts.  Allow  the  current  to  act  through 
the  night.  The  deposit  will  be  light  in  color  and  very 
adherent. 

Classen  has  discovered  that  a  tin  solution  containing  an 
excess  of  ammonium  sulphide,  largely  diluted  with  water, 
yields  a  quantitative  deposition  of  the  metal  when  ex- 
posed to  the  action  of  a  current  from  two  Bunsen  cells. 
In  dilute  sodium  or  potassium  sulphide  solution  the  tin 
precipitation  is  incomplete,  and  whenever  such  conditions 
exist,  the  sodium  or  potassium  salt  must  be  converted  into 
ammonium  sulphide.  To  this  end  the  liquid  is  mixed 
with  about  25  grams  of  ammonium  sulphate,  free  from 
iron,  and  the  solution  then  carefully  warmed  in  a  covered 
vessel  until  the  evolution  of  hydrogen  sulphide  ceases; 
after  which  the  liquid  is  heated  to  incipient  ebullition  for 
fifteen  minutes.  Allow  it  to  cool,  dissolve  any  sodium 
sulphate  which  may  have  separated  by  the  addition  of 


I  I  4  ELECTRO-CHEMICAL   ANALYSIS. 

water,  and  electrolyze.  The  tin  separates  in  a  gray, 
dense  layer.  Wash  it  with  water  and  alcohol.  At  times 
sulphur  sets  itself  upon  the  tin  deposit ;  this  is  difficult  to 
remove,  but  can  be  detached,  after  washing  the  deposit 
with  alcohol,  by  gently  applying  a  linen  handkerchief. 
Having  potassium  sulphostannate,  Classen  considers  it 
advisable  to  convert  the  tin  into  oxalate  and  then  electro- 
lyze. He  employs  two  methods.  One  will  be  given 
here : — 

Decompose  the  greater  portion  of  the  sulpho-salt  with 
dilute  sulphuric  acid  (the  liquid  must  remain  alkaline)  to 
get  rid  of  most  of  the  sulphur  as  hydrogen  sulphide,  then 
oxidize  with  hydrogen  peroxide  until  the  metastannic  acid 
produced  is  pure  white  in  color.  Acidulate  with  sulphuric 
acid,  neutralize  with  ammonia  water,  and  again  add  hy- 
drogen peroxide.  Filter  out  the  stannic  acid  when  it  has 
subsided,  dissolve  in  oxalic  acid  and  ammonium  oxalate, 
and  electrolyze  with  the  conditions  given  in  the  preceding 
paragraphs. 

According  to  Carl  Engels  add  0.3  to  0.5  gram  of  hy- 
droxylamine  hydrochloride  or  sulphate,  2  grams  of  ammo- 
nium acetate,  and  2  grams  of  tartaric  acid  to  the  solution 
of  the  tin  salt,  dilute  with  water  to  150  c.c.,  heat  to  6o°- 
70°,  and  electrolyze  with  N.D100  =  i  ampere. 


DETERMINATION    OF    METALS ANTIMONY.  I  I  5 


ANTIMONY. 

LITERATURE. — Wrightson,  Z.  f.  a.  Ch.,  15,  300;  Parodi  and  Mascaz- 
zini,  Z.  f.  a.  Ch.,  18,  588;  Luckow,  Z.  f.  a.  Ch.,  19,  13  ;  C lassen  and  v. 
Reiss,  Ber.,  14,  1622;  17,2467;  18,  1104;  Lecrenier,  Ch.  Z.,  13,  1219; 
Chittenden,  Pro.  Conn.  Acad.  Sci.,  Vol.  8;  Vortmann,  Ber.,  24,  2762; 
Rudorff,  Z.  f.  a.  Ch.,  1892,  199;  Classen,  Ber.,  27,  2060;  Ost  and  K 1  ap- 
pro th,  Z.  f.  ang.  Ch.  (1900),  827. 

Antimony,  when  precipitated  from  a  solution  of  its 
chloride,  or  from  that  of  antimony  potassium  oxalate, 
does  not  adhere  well  to  the  cathode.  It  is  deposited  very 
slowly  from  a  solution  of  potassium  antimonyl  tartrate. 
Its  deposition  from  a  cold  ammonium  sulphide  solution  is 
satisfactory,  but  the  use  of  this  reagent  for  this  purpose  is 
not  pleasant,  especially  when  several  analyses  are  being 
carried  out  simultaneously.  For  .this  reason  potassium 
or  sodium  sulphide  has  been  substituted.  The  alkaline 
sulphide  used  must  not  contain  iron  or  alumina. 

The  antimony  solution,  mixed  with  80  c.c.  of  sodium 
sulphide  (sp.  gr.  1.13-1.15),  should  be  diluted  with  water 
to  125  c.c.  and  acted  upon  at  6o°-65°  with  a  current  of 
N.D100  =  i  ampere  and  1.1—1.7  volts.  The  metal  will  be 
fully  precipitated  in  two  hours.  The  deposit  should  be 
treated  in  the  usual  way  with  water  and  pure  alcohol. 
Dry  at  90°.  To  ascertain  when  all  of  the  metal  has  been 
deposited,  incline  the  dish  slightly,  thus  exposing  a  clean 
platinum  surface.  If  this  remains  bright  for  half  an  hour 
the  precipitation  is  finished.  In  separating  antimony 
from  the  heavy  metals — e.  g. ,  lead — it  happens  that  alka- 
line sulphides  containing  poly  sulphides  are  used,  or  are 
produced.  To  remove  these  Classen  proposed  adding  to 
the  antimony-polysulphide  mixture,  already  in  a  weighed 
platinum  dish,  an  ammoniacal  solution  of  hydrogen  per- 


I  1  6  ELECTRO-CHEMICAL    ANALYSIS. 

oxide,  and  warming  the  same  until  the  liquid  becomes 
colorless.  When  this  is  accomplished,  even  if  a  precipi- 
tate has  been  produced,  add,  after  cooling,  the  solution  of 
sodium  monosulphide,  and  electrolyze  as  previously 
directed. 

Lecrenier  writes  as  follows  relative  to  the  preceding 
method :  The  precipitation  is  all  that  one  can  desire,  pro- 
viding the  solution  of  the  sulpho-salt  is  absolutely  free 
from  polysulphides ;  otherwise,  it  is  incomplete.  The 
antimony  sulphide  obtained  in  the  ordinary  course  of 
analysis  always  contains  sulphur,  and  this  must  be  elimi- 
nated. To  remove  the  various  inconveniences  connected 
with  the  method  add  50-70  c.c.  of  a  25  per  cent,  solution 
of  sodium  sulphite  to  the  solution  after  the  addition  of  the 
excess  of  sodium  sulphide,  then  heat  the  liquid  to  com- 
plete decolorization ;  allow  to  cool,  after  which  the  current 
is  conducted  through  the  liquid.  This  can  rise  to  0.5 
ampere  without  impairing  the  result;  but  it  is  not  best, 
as  the  precipitated  metal  is  then  not  very  coherent.  It  is 
better  to  use  a  current  of  0.25  ampere.  When  the  quan- 
tity of  antimony  does  not  exceed  0.2  gram,  the  deposit 
will  be  adherent  and  free  from  sulphur;  wash  with  water, 
alcohol,  and  ether.  Sulphur  will  separate  upon  the  anode, 
despite  the  presence  of  an  excess  of  sodium  sulphite. 
This,  however,  does  not  affect  the  result. 

The  method  of  Classen  suffers  in  several  points : 

1.  The  bath  pressure  falls  as  the  electrolysis  proceeds, 
because  of  the  accumulation  in  it  of  sodium  polysulphide. 

2.  If  the  electrolysis  is  not  interrupted  at  the  proper 
moment,  antimony  already  precipitated  will  be  again  dis- 
solved by  the  polysulphide  which  has  diffused  toward  the 
cathode  (Z.  f.  ang.  Ch.,  1897,  325).     Ost  and  Klapproth 
have  sought  by  the  use  of  a  diaphragm  to  circumvent 


DETERMINATION    OF    METALS ANTIMONY. 


117 


these  objectionable  features.  To  this  end  they  use  (Fig. 
37)  a  roughened  dish,  a,  in  which  is  suspended  a  dish- 
shaped  diaphragm,  b  (a  Pukall  porous  cup,  Ber.,  26,  1 159). 
A  strip  of  platinum,  c,  within  the  diaphragm,  is  the  anode, 
while  the  platinum  dish  itself  constitutes  the  cathode. 
Cover-glasses  are  placed  over  both  dishes.  The  liquids 


FIG.  37. 


experimented  upon  were  a  solution  of  Schlippe's  salt 
(=  0.0985  gram  of  antimony  in  10  c.c.)  and  a  solution  of 
pure  sodium  sulphide  (195  grams  Na2S  =  200  grams 
NaOH  to  the  litre).  In  the  first  experiments  the  anti- 
mony was  equally  distributed  in  the  whole  electrolyte. 
The  cathode  chamber  contained  85  c.c.  and  the  anode 
chamber  40  c.c.  of  the  solution,  which  had  0.0985  gram  of 
antimony  in  125  c.c.,  with  varying  amounts  of  sodium 


n8 


ELECTRO-CHEMICAL    ANALYSIS. 


sulphide.     The  liquid  covered  about  100  sq.  cm.  of  the 
surface  of  the  dish : — 


BATH  PRESSURE 

CURRENT  STRENGTH 

EXPERI- 
MKNT. 

NaoS 
SOLU- 
TION. 

TEMPERA- 
TURE. 

AT  i  AMPERE. 

IN  AMPERES. 

ANTI- 
MONY 
PRECIPI- 
TATED. 

BEGINNING 

END 

AT  BEGIN- 

AT 

VOLTS. 

VOLTS. 

NING. 

END. 

j 

5  c.c. 

70° 

3-8 

3-9 

0.7 

0-3 

0.0675 

2 

50     «« 

Cold 

1.9 

3-8 

0-5 

0.4 

0.0725 

3 

80     " 

70° 

2-5 

1-7 

I.O 

I.O 

0.0685 

4 

80     « 

70° 

1-7 

-.3 

I.O 

I.O 

0.0720 

When  the  electrolysis  was  finished,  antimony  could  not 
be  found  in  the  cathode  liquid  from  any  one  of  the  four 
experiments,  whereas  in  the  anode  chamber  it  was  still  in 
solution,  and  in  experiment  i  it  had  been  precipitated  on 
the  anode  in  the  form  of  antimony  pentasulphide. 

These  experiments  indicated  then  that  the  current  is 
not  able  to  carry  antimony  ions  from  the  anode  into  the 
cathode  chamber. 

In  the  next  series  of  experiments  the  10  c.c.  of  antimony 
solution  (=  0.0985  gram  of  metal)  were  placed  in  the 
cathode  chamber  alone : — 


BATH  PRESSURE  AT  i 

AMPERE. 

ANTI- 

EXPERI- 
MENT. 

NaoS 
SOLU- 
TION. 

TEMPERA- 
TURE. 

TIME. 

MONY 
PRECIPI- 
TATED. 

BEGINNING 

AT  END 

VOLTS. 

VOLTS. 

I 

5° 

Cold 

4.2 

3-7 

5  hours 

0.0970 

2 

5° 

7o° 

2.O 

3-8 

3     " 

0.0984 

Temp.  32° 

3 

80 

70° 

2-5 

i-7 

2       " 

0.0990 

4 

50 

70° 

1.8 

1.8 

'i     " 

0.0990 

1 

DETERMINATION    OF    METALS ANTIMONY.  I  I  9 

The  results  show  a  quantitative  precipitation  of  the 
antimony.  None  of  it  could  be  found  either  in  the 
cathode  or  anode  liquid. 

On  placing  the  antimony  in  the  anode  chamber  alone, 
not  a  particle  of  metal  was  deposited  on  the  cathode. 

When  the  antimony  was  placed  in  the  cathode  chamber 
only  and  varying  quantities  of  sodium  sulphide  solution 
were  mixed  with  it,  remarkable  differences  were  observed. 
In  the  presence  of  much  sodium  sulphide  and  accompany- 
ing low  bath  pressure  all  of  the  antimony  was  precipitated 
at  the  cathode,  while  with  little  sodium  sulphide  and  con- 
sequent high  bath  pressure,  a  small  amount  of  antimony 
wandered  through  the  diaphragm  and  was  deposited  at 
the  anode  in  the  form  of  antimony  sulphide. 

These  experiments  show  how  a  successful  antimony 
determination  may  be  made.  No  difficulties  attend  its 
estimation  in  this  way. 

Vortmann,  recognizing  the  fact  that  it  is  difficult  to 
obtain  an  adherent  deposit  of  antimony  when  the  quantity 
of  metal  in  solution  exceeds  o.  16  gram,  has  combined  the 
method  of  Smith,  who  first  pointed  out  that  mercury 
could  be  deposited  very  satisfactorily  from  its  solution  in 
sodium  sulphide,  with  his  knowledge  that  antimony  could 
be  precipitated  from  a  similar  solution,  and  hence  recom- 
mends the  determination  of  the  antimony  in  the  form  of 
an  amalgam.  No  difficulties  attend  this  procedure.  Two 
parts  of  mercury  should  be  present  for  every  part  of  anti- 
mony. The  latter  must  also  be  present  in  solution  as 
higher  oxide;  to  this  end  digest  the  antimonious  solution 
with  bromine  water,  and  afterward  add  the  sodium  sul- 
phide containing  sodium  hydroxide.  Electrolyze  with  a 
current  of  from  0.2  to  0.3  ampere.  The  amalgam  can  be 
washed  in  the  usual  way. 


I2O  ELECTRO-CHEMICAL    ANALYSIS. 


ARSENIC. 

LITERATURE. — Luckow,  Z.  f.  a.  Ch.,  19,  14;  Classen  and  v.  Reiss, 
Ber.,  14,  1622  ;  M core,  Ch.  News,  53,  209  ;  Vortmann ,  Ber.,  24,  2764. 

A  successful  method  for  the  complete  deposition  of 
arsenic  is  not  known.  The  current  acting  upon  the 
chloride  causes  complete  volatilization  of  the  metal  in  the 
form  of  arsine.  Its  separation  from  oxalate  solutions  is 
incomplete;  nor  do  the  sulpho-salts  answer  for  electro- 
lytic purposes. 

From  a  solution  containing  0.2662  gram  of  arsenious 
oxide  Vortmann  obtained  o.  1 8527  gram  of  metallic  arsenic, 
equivalent  to  69.59  Per  cent.  The  trioxide  contains  75.78 
per  cent,  of  arsenic.  This  precipitation  was  effected  by 
the  amalgam  method. 


2.  SEPARATION  OF  THE  METALS. 

Electrolysis,  to  be  of  value,  must  not  only  furnish  the 
analyst  with  methods  suitable  for  the  complete  deposition 
of  metals,  but  it  should,  in  addition,  enable  him  to  sepa- 
rate metallic  mixtures.  The  data  given  in  the  preceding 
pages  will  serve  for  this  purpose,  but,  as  a  special  treat- 
ment is  required  in  some  instances,  a  brief  outline  of  a 
series  of  separations  will  be  indicated. 

It  will  be  noticed  that  the  electrolytes  vary.  The 
mineral  acid  and  the  double  cyanide  solutions  are  best 
adapted  for  the  purpose.  The  greatest  number  of  sepa- 
rations have  been  made  by  means  of  them.  Some  of  the 
organic  acids,  too,  answer  quite  well  as  will  be  seen  in  the 
succeeding  paragraphs. 


SEPARATION    OF    METALS COPPER.  121 


COPPER. 

Inasmuch  as  the  electrolytic  precipitation  of  copper 
gives  the  analyst  such  an  excellent  means  of  determining 
this  metal  quantitatively,  its  separations  from  other  metals 
are  of  prime  importance.  Such  separations,  so  far  as  they 
have  been  carefully  worked  out  in  the  most  essential 
points,  are  given  in  detail  in  the  following  paragraphs. 
It  is  needless  to  add  that  acid  solutions  mainly  are  best 
adapted  for  these  separations. 

1.  From  Aluminium:— 

(a)  In  nitric  acid  solution.     Dilution,  200  c.c. ;  5  c.c.  of 
nitric  acid  (sp.gr.  1.30);  temperature,  32°;  N.D100  = 
i  ampere  and  3.3  volts;  time,  4  hours. 

(b)  In  sulphuric  acid  solution.     Dilution,  150  c.c. ;  3  c.c. 
of  concentrated   sulphuric   acid;  temperature,    59°; 
N.D100  =  i  ampere  and  2.5  volts;  time,  2  hours. 

(c)  In  phosphoric  acid  solution.     Dilution,  225  c.c.;  5 
c.c.  of  phosphoric  acid  (sp.  gr.  1.347);  temperature, 
77°  C. ;  N.D100  =  0.068  ampere  and  2.6  volts;  time,  6 
hours.     Sixty  cubic  centimetres  of  disodium  hydro- 
gen phosphate  (sp.  gr.  1.0338)  were  present  for  0.1239 
gram  of  copper  and  o.iooo  gram  of  aluminium.     The 
precipitated    copper  weighed  0.1240  gram    (J.  Am. 
Ch.  S.,  21,  1002). 

2.  From  Antimony:— 

In  tartrate  solution.  In  the  presence  of  one-tenth 
of  a  gram  of  each  metal,  making  certain  that  the  anti- 
mony is  in  its  highest  state  of  oxidation,  add  8  grams 
of  tartaric  acid  and  30  c.c.  of  ammonia  (sp.  gr.  0.91). 
Electrolyze  at  50°  with  a  current  of  N.D100  =  0.08- 
o.io  ampere  and  1.8-2  volts.  Total  dilution  150  c.c. 


122 


ELECTRO-CHEMICAL    ANALYSIS. 


The  ordinary  temperature.     Time,  5  hours  (J.  Am. 
Ch.  S.,  15,  195)- 

Smith  and  Wallace  (Jr.  An.  Ch.,  7,  189;  Z.  f.  anorg. 
Ch.,  4,  274)  have  also  used  this  separation  with  emi- 
nent success.  They,  too,  emphasize  the  necessity  of 
having  the  antimony  in  its  highest  form  of  oxidation. 
Several  examples  will  illustrate  their  method  of  pro- 
cedure : — 


COPPER 

TAR- 

I 

PRES- 
ENT, 

IN 

GRAMS. 

MONY, 
IN 

GRAMS. 

DILU- 
TION. 

VOL.  OF 
AMMONIA 
(Sp.  GR.  0.932). 

TARIC 

ACID, 

IN 

GRAMS. 

VOLTS. 

N.D100 
=  AMP. 

COPPER 
FOUND. 

0.0670      0.1449 

I75C.C. 

15  c.c. 

3-4 

1.8 

O.I 

0.0670 

0.1341      0.1449 

175   " 

15    " 

3-4 

2.O 

O.I 

0.1341 

0.1341 

0.2898 

175    " 

15    " 

3-4 

2.0 

0.08 

0.1344 

The  deposited  metal  showed  no  antimony. 

3.  From  Arsenic:— 

(a)  In  ammoniacal  solution.  McCay  (Ch.  Z.,  14,  509) 
observed  that  a  current  conducted  through  a  potas- 
sium arsenate  solution,  made  distinctly  ammoniacal, 
had  no  effect  upon  the  arsenic,  while  with  copper 
under  like  conditions  the  metal  was  quantitatively 
precipitated.  Upon  this  behavior  he  has  based  a  very 
excellent  separation  of  the  two  metals.  Care  should 
be  taken  not  to  introduce  too  much  ammonia  water. 
In  this  laboratory  the  method  of  McCay,  with  the 
conditions  here  presented,  has  repeatedly  given  ex- 
cellent results : — 

Add  20  c.c.  of  ammonium  hydroxide  (sp.  gr.  0.91) 
and  2.5  grams  of  ammonium  nitrate  to  the  solution 
containing  0.2121  gram  of  copper  and  0.1540  gram  of 


SEPARATION    OF    METALS COPPER.  123 

arsenic;  dilute  to  125  c.c.  with  water,  heat  to  5o°-6o°, 
and  electrolyze  with  N.D100  ==0.5  ampere  and  3.5 
volts.  The  copper,  precipitated  in  three  hours, 
weighed  0.2123  and  0.2121  gram.  Drossbach  (Ch. 
Z.,  16,  819)  and  Oettel  confirm  (Ch.  Z.  (1890),  14, 
509)  (also  see  Copper)  McCay's  experience. 

Freudenberg,  who  adopted  the  suggestion  of  Kili- 
ani,  of  giving  more  attention  to  the  pressure  than  to 
the  amperage,  succeeded  in  separating  copper  and 
arsenic  (latter  existing  as  arsenate)  by  arranging  to 
have  in  their  solution,  30  c.c.  in  excess  of  a  10  per 
cent,  ammonia  solution  and  then  electrolyzing  with 
a  current  of  1.9  volts  until  the  liquid  became  color- 
less, which  usually  occurred  after  from  6-8  hours  (Z. 
f.  ph.  Ch.,  12,  118). 

Schmucker  separated  copper  from  arsenic  with 
conditions  similar  to  those  indicated  for  copper  and 
antimony  in  ammoniacal  tartrate  solution  (see  above). 

(b)  In  potassium   cyanide  solution.     Add   the   copper 
solution  to  that  of  the  alkaline  arsenite  or  arsenate, 
and  then  introduce  a  solution  of  potassium  cyanide 
until  the  precipitate  first  produced  is  just  dissolved; 
the  liquid  will  then  show  a  slight  purple  tint.     Elec- 
trolyze   with    the    following    conditions:    N.D100  = 
0.25-0.26  ampere;  volts  =  3.4-3.6;  dilution,  150  c.c. ; 
time,  3  hours;  temperature,  60°. 

(c)  In  acid  solution.     Freudenberg  adds  10-20  c.c.  of 
dilute  sulphuric  acid  to  the  solution  of  the  metals 
in  question  and  then  electrolyzes  with  a  current  hav- 
ing a  tension  of  1.9  volts.     The  arsenic  existed  partly 
as  trioxide  and  partly  as  pentoxide.     The  precipita- 
tion was  made  during  the  night  (Z.  f.  ph.  Ch.,  12, 
117).     Copper  present,  0.3000  gram;  found,  0.2997 


I  24  ELECTRO-CHEMICAL    ANALYSIS. 

gram;    arsenic  present,  0.3531   gram.     The    copper 
was  always  brilliant  in  color. 

The  separation  can  also  be  made  in  nitric  acid 
solution  with  the  same  voltage.  It  is  inferior  to  the 
first  method. 

4.  From  Barium,  Strontium,  Calcium,  Magnesium,  and  the 
Alkali  Metals.     The  conditions  given  for  the  separation 
of  copper  from  aluminium  in  nitric  acid  solution  (p.  121) 
will  serve  for  its  separation  from  these  metals. 

5.  From  Bismuth.     See  the  separation  of  bismuth  from 
copper,  p.  158. 

6.  From  Cadmium:— 

(a)  In  nitric  acid  solution.     It  was  in  a  solution  contain- 
ing free  nitric  acid  that  these  two  metals  were  first 
separated  electrolytically  (Am.  Ch.  Jr.,  2,  41).     The 
results  have  been  frequently  confirmed.     An  idea  of 
the  proper  working  conditions  may  be  obtained  from 
the  following :  To  a  solution  in  which  were  present 
0.0988  gram  of  copper  and  0.1152  gram  of  cadmium 
were  added  2  c.c.  of  nitric  acid  of  sp.  gr.  1.43.     The 
total    dilution    of  the    liquid    equaled   100  c.c.     It 
was  heated  to  50°  and   electrolyzed  with   N.D100  = 
o.io  ampere  and  2.5  volts.     In  3  hours  the  copper 
was  completely  precipitated.     It  was  bright  in  color 
and  weighed  0.0988  gram.    It  contained  no  cadmium 
(J.  Am.  Ch.  S.,  19,  873;  also  Jr.  An.  Ch.,  7,  253). 

When  the  copper  has  been  precipitated,  washed, 
dried,  and  weighed,  make  the  residual  liquid  alkaline 
with  sodium  hydroxide,  add  sufficient  potassium  cy- 
anide to  redissolve  the  precipitate,  and  electrolyze 
as  directed  on  p.  68. 

(b)  In    sulphuric    acid    solution.     From    solutions    in 
which  there  is  free  sulphuric  acid  the  copper  may  be 


SEPARATION    OF    METALS COPPER.  125 

electrolytically  precipitated,  leaving  the  cadmium. 
This  is  evidenced  by  the  following  examples:  Total 
dilution,  100  c.c.;  10  c.c.  of  sulphuric  acid,  sp.  gr. 
1.09;  0.1975  gram  of  copper  and  0.1828  gram  of  cad- 
mium; N.D100  =  =  0.05-0.07  ampere  and  1.70-1.76 
volts;  at  the  ordinary  temperature.  The  precipitate 
of  copper  weighed  0.1976  gram  (Am.  Ch.  Jr.,  12, 
no).  By  heating  the  electrolyte  the  time  can  be 
reduced  to  8  hours. 

The  separation  has  also  been  made  by  strict  atten- 
tion to  difference  in  potential  (Freudenberg,  Z.  f.  ph. 
Ch.,  12,  116).  Ten  to  twenty  cubic  centimetres  of 
dilute  sulphuric  acid  are  added  to  the  solution  con- 
taining the  two  metals  and  the  liquid  is  then  electro- 
lyzed  with  a  current  not  exceeding  2  volts.  The 
copper  will  be  deposited  very  rapidly  and  be  free 
from  cadmium. 


COPPER  TAKEN. 
0.2734  gram 
0.4101      " 
o.  3000     '  ' 

CADMIUM  TAKEN. 
0.2560  gram 
0.2958      " 
0.4437      « 

COPPER  FOUND. 
0.2729  gram 
0.4098      " 
0.3003     " 

These  separations  were  conducted  during  the  night. 
Heidenreich  (Ber.,  29,  1585)  met  with  success  in  ap- 
plying Freudenberg's  suggestion,  but  asserts  that 
the  tension  should  not  exceed  1.8  volts  for  N.D100  = 
0.07-0.05  ampere. 

(c)  In  phosphoric  acid  solution.  The  separation  of  the 
two  metals  in  the  presence  of  free  phosphoric  acid  has 
often  been  made  in  this  laboratory  with  satisfaction. 
Favorable  conditions  will  be  found  in  the  example 
which  appears  here:  Dilution  of  solution,  125  c.c.; 
0.2452  gram  of  metallic  copper  and  0.1827  gram  of 


126  ELECTRO-CHEMICAL    ANALYSIS. 

metallic  cadmium;  20  c.c.  of  disodium  hydrogen 
phosphate,  sp.  gr.  1.0353,  and  10  c.c.  of  phosphoric 
acid,  sp.  gr.  1.347;  temperature,  60°;  N.D100  =  0.07- 
0.08  ampere  and  2.5  volts;  time,  3  hours  (Am.  Ch.  Jr., 

12,  329).  ^ 

7.  From  Calcium.     See  the  separation  of  copper  from 

barium,  p.  124. 

8.  From  Chromium.    See  copper  from  aluminium,  p.  121, 

for  the  conditions  of  separation  when  the  metals  are 
present  in  nitric  or  sulphuric  acid  solution. 
(a)  In  phosphoric  acid  solution.  Volume  of  solution 
(containing  0.1239  gram  of  metallic  copper  and 
0.1403  gram  of  metallic  chromium  as  sulphates) 
225  c.c.,  60  c.c.  of  disodium  hydrogen  phosphate  (sp. 
gr.  1.033)  and  8  c.c.  of  phosphoric  acid  (sp.  gr.  1.347); 
N.D100  ==  0.062  ampere  and  2.5  volts;  temperature, 
65°;  time,  6  hours  (J.  Am.  Ch.  S.,  21,  1003). 

9.  From  Cobalt: — 

(a)  In  the  presence  of  nitric  or  sulphuric  acid  the  sepa- 
ration of  these  two  metals  may  be  accomplished  by 
observing  the  conditions  given  for  the  separation  of 
copper  from  aluminium  in  the  presence  of  the  same 
acids  (see  p.  121).  Dr.  Wolcott  Gibbs  employed 
mineral  acid  solutions  for  this  purpose  many  years 
ago  (2.  f-  a.  Ch.,  3,  334).  Most  analysts  prefer  the 
sulphate  solution.  Neumann  is  of  this  number. 
He  dissolves,  for  example,  i  gram  each  of  copper  sul- 
phate and  cobalt  sulphate  in  the  requisite  volume  of 
water,  adds  3  c.c.  of  concentrated  sulphuric  acid, 
dilutes  to  150  c.c. ,  and  electrolyzes  with  N.D100  =  i 
ampere  at  the  ordinary  temperature.  The  time 
required  for  the  complete  precipitation  of  the  copper 
varies  from  2^-3  hours.  The  filtrate  or  solution 


SEPARATION    OF    METALS COPPER.  127 

poured  off  from  the  deposit  of  copper  need  only  be 
mixed  with  an  excess  of  ammonia  water  and  then 
be  exposed  to  a  stronger  current  in  order  to  pre- 
cipitate the  cobalt. 

(6)  In  oxalic  acid  solution.  The  double  oxalates  have 
also  been  used.  The  method  requires  a  strict  adher- 
ence to  the  prescribed  voltage  (1.1-1.3)  to  yield  a 
satisfactory  result.  Classen,  with  whom  the  method 
originated,  advises  the  addition  of  6  grams  of  am- 
monium oxalate  to  the  solution  of  the  salts  and  acid- 
ulates the  liquid  with  oxalic  acid,  acetic  acid,  or  tar- 
taric  acid.  Four  hours  are  required  for  the  precipi- 
tation of  0.25  gram  of  copper  (Z.  f.  Elektrochem.,  1, 
291,  292;  Ber.,  27,  2060). 

(c)  In  phosphoric  acid  solution.  An  example  will 
afford  an  idea  of  the  method  of  procedure:  Total 
dilution,  225  c.c.;  60  c.c.  of  sodium  hydrogen  phos- 
phate (sp.  gr.  1.033);  IO  c-c-  °f  phosphoric  acid  (sp. 
gr.  1.347);  N.D100  =  0.035  ampere  and  1.5  volts; 
temperature,  62°;  time,  6  hours.  Copper  present, 
0.1239  gram;  cobalt  present,  o.iooo  gram.  Copper 
found,  0.1243  gram  (J.  Am.  Ch.  S.,  21,  1003;  Am. 
Ch.  Jr.,  12,329;  Jr.  An.  Ch.,  5,  133). 

10.  From  Gold.     See  p.  175. 

11.  From  Iron:— 

(a)  In  nitric  acid  solution.     The  conditions  given  for 
the  separation  of  copper  from  aluminium  (p.  121)  will 
answer  here.     When  much  iron  is  present,  difficul- 
ties will  be  encountered.     The  copper  tends  to  redis- 
solve  (Schweder,  Berg-Hiitt.  Z.,  36,  5,  n,  31). 

(b)  In  sulphuric  acid  solution.     Experience   has    dem- 
onstrated that  the  separation  of  the  metals  in  ques- 
tion is  best  and  most  accurately  made  in  the  presence 


128  ELECTRO-CHEMICAL    ANALYSIS. 

of  free  sulphuric  acid,  observing  the  conditions  as 
described  on  p.  1 2 1  for  copper  from  aluminium.  When 
the  copper  has  been  fully  precipitated,  which  usually 
requires  2^  hours,  the  residual  solution  is  poured  off, 
the  copper  is  washed,  and  the  liquid  reduced  to  a 
suitable  volume,  neutralized  with  ammonia,  and  4-6 
grams  of  ammonium  oxalate  introduced  into  the 
liquid,  which  is  then  electrolyzed  at  30°-  40°  with  a 
current  of  N.D100  =  1-1.5  amperes  and  3.4-3.8  volts. 
The  iron  will  be  fully  precipitated  in  3-4  hours  (Clas- 
sen, Neumann). 

(c)  In  phosphoric  acid  solution.     In  this  laboratory  suc- 
cess has  attended  the  use  of  the  phosphates  in  the 
presence  of  free  phosphoric  acid.    Recently  the  proper 
conditions  as  to  current  density  and  voltage  have 
been  carefully  determined.     It  will  be  seen  from  the 
appended  example  that  the  results  are  most  satisfac- 
tory: Total   dilution,    225   c.c.;  disodium   hydrogen 
phosphate,  60  c.c.  (sp.  gr.  1.0358);  10  c.c.  of  phos- 
phoric  acid    (sp.    gr.    1.347);  temperature,    53°   C. ; 
N.D100=  0.04  ampere  and  2.4  volts;  time,  7  hours. 
Copper  present,   0.1239  gram;  found,  0.1237  gram 
(Am.  Ch.  Jr.,  12,  329;  Jr.  An.  Ch.,  5,  133;  J.  Am. 
Ch.  S.,  21,  1002). 

(d)  In  ammoniacal  solution.     In  such  a  solution  Vort- 
mann  separates  the  copper  from  a  large  quantity  of 
iron.     The  liquid  containing  the  two  metals  is  mixed 
with  ammonium  sulphate  and  an  excess  of  ammonia 
water.    The  author  maintains  that  the  ferric  hy- 
droxide, which  is  of  course  precipitated,  does  not  in- 
terfere with  the  deposition  of  the  copper.     The  latter 
is  free  from  iron.      The  current  employed  in  this 
separation  should  be  N.D100   =  0.1-0.6  ampere  (M.  f. 
Ch.,  14,  552). 


SEPARATION    OF    METALS COPPER.  I  29 

It  is  doubtful  whether  the  copper  is  really  free 
from  iron.  The  opinion  presented  under  the  separa- 
tion of  nickel  from  iron  (p.  186)  and  the  experiences 
there  recorded  certainly  make  this  recommendation 
very  questionable.  Indeed,  in  this  laboratory  it  was 
found  in  separating  the  copper  from  iron  in  chalco- 
pyrite  by  this  method  that  if  the  precipitation  of  the 
former  took  place  in  a  platinum  dish  it  was  invariably 
contaminated  with  iron.  On  the  other  hand,  if  the 
solution  of  metals  was  placed  in  a  beaker-glass  and 
a  vertical  platinum  plate  was  made  the  cathode, 
then  the  copper  deposited  was  free  from  iron.  The 
ferric  hydrate  floating  about  in  the  platinum  dish  and 
in  immediate  contact  with  the  precipitate  is  partially 
reduced  to  the  metallic  form. 

(e)  In  oxalic  acid  solution.  This  procedure  is  due  to 
Classen  (Ber.,  27,  2060),  who  adds  to  the  solution 
containing  both  metals  in  the  form  of  sulphates  from 
6-8  grams  of  ammonium  oxalate  and  sufficient 
oxalic,  acetic,  or  tartaric  acid  to  render  the  liquid 
acid.  The  total  dilution  is  150  c.c.  N.D100  =  i 
ampere;  voltage,  2.9-3.4  at  5o°-6o°.  Time,  3  hours. 
It  is  absolutely  necessary  to  replace  the  oxalic  acid  as 
it  is  decomposed,  otherwise  iron  will  separate  upon 
the  copper.  The  method  requires  the  strictest  atten- 
tion to  details,  otherwise  its  results  will  be  far  from 
satisfactory.  Indeed,  its  omission  from  the  last  edi- 
tion of  Classen's  "Quantitative  Electrolysis"  would 
seem  to  indicate  that  its  author  had  lost  faith  in  its 
efficacy. 

12.  From  Lead.  The  separation  of  these  two  metals  has 
great  value  from  the  technical  standpoint.  It  is 
fortunate,  therefore,  while  both  separate  under  the 


130  ELECTRO-CHEMICAL   ANALYSIS. 

influence  of  the  current  in  a  nitric  acid  solution,  that 
they  are  deposited  at  opposite  poles.  Very  consid- 
erable attention  has  been  paid  to  the  conditions 
which  ought  to  prevail  during  the  deposition.  Many 
writers  have  contributed  their  experience  on  this 
point,  and  from  them  is  gathered  the  following :  The 
liquid  electrolyzed  should  equal  150  c.c.  in  volume. 
It  should  contain  15  c.c.  of  nitric  acid  and  be  heated 
to  about  60°  and  acted  upon  with  a  current  of  N.D100 
=  1-1.5  amperes  and  1.4  volts.  In  the  course  of 
an  hour  all  the  lead  will  have  been  precipitated  upon 
the  anode, — which  in  this  separation  should  be  a  dish 
with  roughened  surface, — but  not  all  of  the  copper  will 
have  been  deposited  on  the  cathode — a  smaller,  per- 
forated dish.  It  will  be  noticed  in  the  course  of  the 
decomposition  that  the  lead  separates  first  and  the 
copper  more  slowly.  When  the  lead  is  fully  precip- 
itated, wash  without  interrupting  the  current,  pro- 
ceed further  as  directed  on  p.  79,  and  after  placing 
the  liquid  and  wash  water  reduced  to  130  c.c.  into 
another  weighed  dish,  make  the  latter  the  cathode 
and  suspend  in  it  the  smaller  dish  upon  which  some 
copper  had  been  deposited,  making  it  the  anode. 
The  solution  will  give  up  its  copper  on  passing  the 
current  and  the  metal  will  be  deposited  on  the  larger 
vessel  (the  cathode).  It  may  be  well  to  add  that  the 
liquid  poured  from  off  the  lead  dioxide  will  be  quite 
acid,  therefore  neutralize  it  with  ammonia  water  and 
add  10  c.c.  of  nitric  acid.  The  electrolysis  can  then  be 
conducted  with  N.D100  =  i  ampere  and  2.2-2.5  volts, 
at  the  ordinary  temperature. 

13.  From  Magnesium.     See  the  separation  of  copper  from 
barium,  etc.,  p.  124. 


SEPARATION    OF    METALS COPPER.  131 

14.  From  Manganese:— 

(a)  In  sulphuric  acid  solution.     It  should  be  remem- 
bered that  from  such  a  solution  the  manganese  will 
be  deposited  upon  the  anode  as  peroxide  (see  p.  96) ; 
therefore,  in  the  electrolysis  let  the  larger  dish,  with 
rough  inner  surface,  be  made  the  anode  to  receive 
the  manganese.     The  solution  containing   the    two 
metals  is  diluted  to  130-150  c.c.  with  the  addition 
of  10  drops  of  concentrated  sulphuric  acid.     L,et  the 
current    be    N.D100    =   0.5-1.0    ampere.     The   most 
favorable    temperature    is    5o°-6o°.     The    time    re- 
quired is  usually  2-3  hours.     Experience  has  taught 
that    too    much    manganese    must    not  be  present. 
When  the  deposition  is  finished,  treat  the  deposit 
as  already  described  on  p.  96.     The  washing  should 
be    performed    without    interrupting    the     current. 

(b)  In  nitric  acid  solution.     The  separation  can  also  be 
effected  in  the  presence  of  free  nitric  acid.     If  the 
content  of  the  latter,  however,  exceeds  3  to  4  per 
cent.,  instead  of  having  the  manganese  precipitated 
on  the  anode  it  remains  in  solution  and  a  red  color 
appears  at  the  anode  due  to  permanganic  acid.     In 
the  actual   analysis,  the  solution  of  the  two  metals 
ought  to  be  acidulated  with  a  few  cubic  centimeters 
of  acid  and  then  electrolyzed  at  60°  with  the  same 
current  conditions  as  given  in  a. 

It  will  be  wise  here  to  observe  the  statement  made 
upon  page  96  as  to  the  influence  of  the  strong  min- 
eral acids.  Indeed,  if  this  be  true,  then  the  preced- 
ing separations  are  worthless  and  should  be  discarded , 
as  has  been  done  with  the  separation  in  oxalate  so- 
lutions. In  the  writer's  personal  experience  the  sepa- 
ration in  sulphuric  acid  solution  does  give  satisfac- 


132  ELECTRO-CHEMICAL    ANALYSIS. 

tory  results.  The  subject  deserves  further  investi- 
gation. 

(c)  In  phosphoric  acid  solution.  When  free  phosphoric 
acid  is  present  in  the  solution  containing  salts  of  these 
metals,  no  question  need  arise  as  to  the  result,  for 
oft-repeated  tests,  made  in  this  laboratory,  have 
amply  demonstrated  the  accuracy  of  the  procedure. 
The  appended  example  will  illustrate:  N.D100 
0.05  ampere;  voltage  2.5;  temperature,  56°; 

time,  6  hours;  dilution,  225  c.c.;  copper  present, 
o.  1 239  gram ;  copper  found,  0.1236  gram ;  manganese 
present,  o.i 200  gram;  60  c.c.  of  disodium  hydrogen 
phosphate  (sp.gr.  1.038);  10  c.c.  of  phosphoric  acid 
(sp.  gr.  1.347)  (J.  Am.  Ch.  S.,  21,  1004,  and  Am. 
Ch.  Jr.,  12,329). 

The  copper  deposit  in  this,  as  well  as  in  the  many 
other  trials  conducted  under  practically  the  same 
conditions,  was  deep  red  in  color  and  very  adherent. 
It  contained  no  manganese.  The  latter  does  not 
even  appear  at  the  anode,  except  as  an  amethyst 
color,  indicating  the  formation  there  of  perman- 
ganic acid. 

15.  From  Mercury.     See  the  separation  of  mercury  from 
copper,  pp.  150,  151. 

16.  From  Molybdenum.     Add    1.5  grams  of  pure  potas- 
sium cyanide  to  the  solution  of  the  two  metals ;  dilute 
with  water  to  150  c.c.,  heat  to  60°,  and  electrolyze  with 
N.D100   =  0.28  ampere  and  4  volts.     The  copper  will 
be  completely  precipitated  in  5-6  hours. 

17.  From  Nickel:— 

(a)  In  acid  solution.  This  separation  may  be  realized 
by  observing  the  conditions  given  for  the  separation 
of  copper  from  aluminium  (p.  121)  or  those  noted 


SEPARATION    OF    METALS COPPER.  133 

under  copper  from  cobalt  (p.  126).  That  is,  in  nitric 
or  sulphuric  acid  solution  (Wolcott  Gibbs,  Z.  f.  a.  Ch., 
3,  334),  the  separation  is  all  that  the  analyst  can  ask. 
The  separation  in  oxalate  solution,  as  recommended 
by  Classen  (Z.  f.  Elektrochem.,  1,  291,  292),  must  also 
be  executed  with  conditions  analogous  to  those  indi- 
cated for  copper  from  cobalt,  b  (p.  127). 
(b)  In  phosphoric  acid  solution.  The  writer  has  found 
that  in  the  presence  of  free  phosphoric  acid  this 
separation  can  be  made  with  ease  and  the  confi- 
dence of  securing  a  favorable  result :  copper  present, 
0.1239  gram;  copper  found,  0.1241  gram;  nickel 
present,  0.1366  gram;  60  c.c.  of  disodium  hydrogen 
phosphate,  sp.  gr.  1.033;  IO  c-c-  °f  phosphoric  acid, 
sp.gr.  1.347;  total  dilution,  225  c.c.;  N.D100  =  0.035 
ampere;  tension  =  1.5  volts;  time,  6  hours;  tempera- 
ture, 62°  C.  (J.  Am.  Ch.  S.,  21,  1003).  For  the  con- 
ditions when  iron,  cobalt,  zinc,  and  copper  are  present 
together  in  phosphoric  acid  solution,  see  J.  Am.  Ch. 
S.,  21,  1004. 

18.  From  Palladium.     See  the  following  separation: 

19.  From  Platinum.     Add  1.5  grams  of  pure  potassium 
cyanide  and  5  grams  of  ammonium  carbonate  to  the 
solution  of  the  two  metals,  dilute  with  water  to  125  c.c., 
heat  to  70°,  and  electrolyze  with  N.D100  =0.2  ampere 
and  2-2.5  volts.     The  copper  will  be  precipitated  in 
6  hours. 

20.  From  Potassium.     See  copper  from  barium,  etc.  (p. 
124). 

21.  From  Selenium.  This  separation  has.  not  been  worked 
out. 

22.  From  Sodium.     See  copper  from  barium,  p.  124. 

23.  From  Strontium.     See  copper  from  barium,  p.  124. 


134  ELECTRO-CHEMICAL    ANALYSIS. 

24.  From  Silver.     See  silver  from  copper,  p.  171.     Classen 
proposed  to  precipitate  the  two  metals  with  ammonium 
oxalate,  silver  oxalate  being  insoluble  in  an  excess  of 
the  precipitant,  while  the  copper  salt  was  soluble.    The 
former  was   to  be  filtered  off,  dissolved  in  potassium 
cyanide,  and  electrolyzed,  while  the  filtrate  containing 
the  copper  was  to  be  subjected  to  a  separate  electrol- 
ysis.    This  is  really  not  an  electrolytic   separation,  as 
was  shown  by  others  (J.  Am.  Ch.  $.,  16,  420).     Fur- 
ther, the  copper  deposits  were  invariably  found  to  con- 
tain silver,  so  that  it  is  best  not  to  follow  this  procedure. 

25.  From  Tellurium  :— 

In  nitric  acid  solution.  For  several  years,  at  intervals, 
experiments  have  been  made  in  this  laboratory  by  D. 
L.  Wallace,  upon  the  electrolytic  separation  of  these 
metals.  The  results  have  been  uniformly  good  with 
the  following  conditions:  Copper,  in  grams,  0.1543; 
tellurium,  in  grams,  o.noi;  dilution,  100  c.c.; 
0.5  c.c.  nitric  acid  (sp.  gr.  1.42);  N.D100  =  o.io 
ampere  and  2.06  volts;  temperature,  66°-7o°; 
time,  5  hours.  Copper  found:  (a)  0.1541  gram;  (b) 
o.i 546  gram;  (c)  0.1543  gram;  (d)  0.1542  gram. 

26.  From  Thallium.     No  attempt  has  been  made  to  effect 
this  separation. 

27.  From    Tin.     Schmucker   demonstrated    (J.  Am.  Ch. 
$.,   15,   195)  that,  having  tin  in  its  highest  oxidation 
form,  it  is  possible  to  precipitate  and  separate  copper 
from  it  by  adding  to  the  solution  8  grams  of  tartaric 
acid  and  30  c.c.  of  ammonia  water  (sp.  gr.  0.91),  then 
electrolyzing  at  50°  C.  with  N.D100  ==  0.04  ampere  and 
1.8  volts.     If  a  tenth  of  a  gram  of  each  metal  be  present, 
the  copper  will  be  precipitated  in  5  hours.     The  total 
dilution  was  175  c.c. 


SEPARATION  OF  METALS COPPER.          135 

As  observed  in  preceding  paragraphs,  this  method 
was  utilized  by  Schmucker  in  the  separation  of  copper 
from  arsenic  and  copper  from  antimony.  The  same 
author  also  separated  copper  from  a  mixture  of  anti- 
mony, arsenic,  and  tin,  using  the  conditions  as  de- 
scribed above. 

Or,  when  antimony,  arsenic,  and  tin  are  associated 
with  copper,  treat  the  four  sulphides  with  sodium  sul- 
phide. The  resulting  alkaline  sulphide  solution  can 
then  be  employed  for  the  separation  of  the  first  three 
(p.  177),  while  the  insoluble  copper  sulphide  may  be 
dissolved  and  treated  as  described  on  p.  65. 

28.  From  Tungsten.     The  conditions  given  for  the  sepa- 
ration of  copper  from  molybdenum  (p.    132)  may  be 
used  for  this  separation. 

29.  From  Uranium:— 

(a)  In  nitric  acid  solution.     Add  0.5  c.c.   of  concen- 
trated nitric  acid  to  the  solution,  dilute  to  150  c.c., 
heat  to  60°,  and  electrolyze  with  N.D100  =  0.14-0.27 
ampere  and  2-2.4  volts.     The  copper  will  be  precip- 
itated in  3  hours. 

(b)  In  sulphuric  acid  solution.     The  solution  of  these 
metals  should  be  mixed  with  2  c.c.  of  concentrated 
sulphuric  acid,  diluted  to  150  c.c.  with  water,  heated 
to   5o°-6o°,   and    electrolyzed  with   N.D100    =    0.16 
ampere  and  2  volts.     The  precipitation  will  be  com- 
plete in  4  hours. 

30.  From  Vanadium.     A  method  of  separation  is  lacking. 

31.  From  Zinc:— 

(a)  In  nitric  acid  solution.  The  conditions  mentioned 
under  a  in  copper  from  aluminium  (p.  121),  and 
under  copper  from  cobalt  (p.  126)  and  nickel  (p.  132), 
will  answer  here  in  getting  a  satisfactory  separation. 


136  ELECTRO-CHEMICAL   ANALYSIS. 

The  solution  must  be  kept  acid  during  the  decompo- 
sition. To  this  may  be  added,  that  to  a  solution  con- 
taining 0.1341  gram  of  copper  and  equal  amounts  of 
zinc,  cobalt,  and  nickel,  5  c.c.  of  nitric  acid  were 
added,  the  liquid  was  diluted  to  200  c.c.,  and  electro- 
lyzed  with  0.04  ampere,  when  0.1339  gram  of  copper 
was  obtained. 

(b)  In    sulphuric    acid    solution.     The    conditions    are 
analogous  to  those  employed  for  the  separation  of 
copper  from  aluminium  (p.  121),  cobalt  (p.  12 6),  and 
nickel  (p.  132). 

(c)  In  oxalate  solution.     This  method  (Ber.,  17,  2467) 
is  no  longer  recommended.     Only  the  most  careful 
observance  of  the  conditions  given  will  yield  anything 
like  a  satisfactory  result. 

(d)  In  phosphoric  acid  solution  (Am.  Ch.  Jr.,   12,  329; 
Jr.  An.  Ch.,  5,  133).     The  early  suggestions  that  these 
metals  be  precipitated  as  phosphates  and  the  latter  be 
then  dissolved  in  phosphoric  acid  and  the  resulting 
solution  be  electrolyzed  were  not  favorably  received. 
Here,  in  this  laboratory,  where  the  separation  had 
been  repeatedly  performed,  the  method  gave  satis- 
faction.    To  extend  its  application  the  most  favor- 
able conditions  have  been  worked  out  and  repeated. 
They  are  given  in  the  example  which  follows : — 

To  the  solution  of  the  sulphates,  containing  0.1239 
gram  of  copper  and  a  like  quantity  of  zinc,  were  added 
60  c.c.  of  disodium  hydrogen  phosphate  (sp.  gr.  1.033) 
and  10  c.c.  of  phosphoric  acid  (sp.  gr.  1.347).  It  was 
diluted  to  225  c.c.,  heated  to  60°,  and  electrolyzed 
with  N.D100  =  0.035  ampere  and  2.5  volts,  for  5 
hours,  when  0.1244  gram  of  copper  was  obtained, 
free  from  zinc. 


SEPARATION    OF    METALS CADMIUM.  137 

Another  interesting  separation,  properly  belong- 
ing here,  was  that  of  copper  from  a  mixture  of  iron, 
cobalt,  and  zinc.  The  solution  diluted  to  225  c.c. 
contained : — 

0.1239  gram  of  copper 

0.1007     "     "    cobalt 

o.  1000     "     "    iron 

o.  1200     "     "    zinc 

30  c.c.  of  Na2HPO4  (sp.  gr.  1.0358) 

15    «    «    H3P04  (sp.  gr.  1.347) 

It  was  electrolyzed  at  57°  with  a  current  of  N.D100  = 
0.04-0.05  ampere  and  2.3  volts.     In  six  hours  the 
copper  was  fully  precipitated.     It  weighed  0.1240 
gram  and  contained  none  of  the  other  metals  (J.  Am. 
Ch.  S.,  21,  1003,  1004). 


CADMIUM. 

The  ordinary  gravimetric  methods  for  the  determina- 
tion of  this  metal  are  such  that  they  can  frequently  with 
advantage  be  replaced  by  the  electrolytic  process.  The 
same  is  true^  when  it  comes  to  the  separation  of  cadmium 
from  the  metals  usually  associated  with  it,  as  well  as  those 
with  which  it  only  occasionally  occurs.  The  writer  prefers 
the  electrolytic  course  whenever  it  is  available.  To  what 
extent  the  various  suggestions  offered  for  the  electrolytic 
determination  of  the  metal  can  be  applied  in  separations 
may  be  gathered  from  the  following  paragraphs : — 

1.  From  Aluminium  :— 

(a)  In  sulphuric  acid  solution.     In  this  separation  it  is 
only  necessary  to  add  to  the  solution  of  the  salts  of  the 


138  ELECTRO-CHEMICAL    ANALYSIS. 

metals  3  c.c.  of  sulphuric  acid,  of  specific  gravity  1.09, 
dilute  to  125  c.c.  with  water,  heat  to  65°,  and  electro- 
lyze  with  N.D100  =  0.078  ampere  and  2.61  volts. 
The  cadmium  will  be  deposited  in  the  course  of  from 
4-4^  hours.  It  should  be  washed  without  interrupt- 
ing the  current.  In  one  case  o. mi  Cd  instead  of 
0.1105  was  found;  in  another,  0.1181  instead  of 
o.  1 1 88  gram ;  and  in  a  third,  o.  1 604  instead  of  o.  1 599 
gram. 

(b)  In  phosphoric  acid  solution.  Add  an  excess  of  di- 
sodium  hydrogen  phosphate  (sp.  gr.  1.0358)  to  the 
solution  of  the  metals  and  then  sufficient  phosphoric 
acid  (sp.  gr.  1.347)  to  leave  about  1.5  c.c.  of  the  latter 
in  excess.  Dilute  with  water  to  100  c.c.,  heat  to 
50°,  and  electrolyze  with  N.D100  =  0.06  ampere  and  3 
volts.  Time,  7  hours.  See  p.  69  for  further  details. 
(J.  Am.  Ch.  S.,  20,  279;  Am.  Ch.  Jr.,  12,  329;  13,  206). 

2.  From  Antimony.     Schmucker  (J.  Am.  Ch.  S.,  15,  195) 
used  for  this  purpose  the  method  described  on   p.  121 
for  the  separation  of  copper  from  antimony,  observing 
the  same  conditions.     The  results  were  perfectly  satis- 
factory.    In  washing  the  cadmium  deposit  water  alone 
was  used.     The  deposition  was  made  during  the  night, 
but  by  heating  the  electrolyte  the  time  factor  can  be 
much  reduced. 

3.  From  Arsenic:— 

(a)  In  ammoniacal  tartrate  solution.  Proceed  precisely 
as  directed  on  p.  123  in  the  separation  of  copper  from 
arsenic  (J.  Am.  Ch.  S.,  15,  195). 

(6)  In  alkaline  cyanide  solution.  After  converting 
the  arsenic  into  its  highest  state  of  oxidation,  add 
from  2  to  3  grams  of  potassium  cyanide  to  the  solu- 
tion containing  the  metals  and  electrolyze  with  a 


SEPARATION    OF    METALS CADMIUM.  139 

pressure  not  exceeding  2.6  volts  (Am.  Ch.  Jr.,  12,  428; 
Z.f.ph.Ch.,  12,122). 

4.  From  Barium,  Strontium,  Calcium,  Magnesium,  and 
the  Alkali  Metals.     No  records  of  any  such  separations 
have  been  made. 

5.  From  Beryllium.     There  is  no  record  of  this  separation. 

6.  From  Bismuth.     See  separation  of  bismuth  from  cad- 
mium, p.  157. 

7.  From  Chromium.     The  conditions  given  for  the  sepa- 
ration of  cadmium  from  aluminium  will  answer  equally 
well  in  this  case. 

8.  From  Cobalt  :— 

(a)  In   sulphuric   acid   solution.     Use    the    conditions 
prescribed    for    the    separation    of    cadmium    from 
aluminium  (p.  137).     It  may  be  well  to  add  that  the 
addition    of    ammonium    sulphate  to  the    solution 
is  advantageous.      The    voltage    should   not  exceed 
2.8-2.9. 

(b)  In  alkaline  cyanide  solution.     Add  4-5  grams  of 
pure  potassium  cyanide  to  the  solution  of  the  metals, 
dilute  to  200  c.c.,  and  electrolyze  with  N.D100  =  0.3 
ampere  and  2.6  volts  (Am.  Ch.  Jr.,  12,  104;  Z.  f.  ph. 
Ch.,  12,  116). 

9.  From  Copper.     See  also  copper  from  cadmium,  pp.  124, 
125.   In  addition  to  the  methods  used  in  separating  these 
metals,  in  which  the  copper  is  precipitated,  we  may  add 
the  following :  Introduce  5  to  6  grams  of  pure  potassium 
cyanide  into  the  solution  of  the  metals  for  every  0.2- 
0.4  gram  of  cadmium  and  copper.    Dilute  the  solution  to 
200  c.c.  and  electrolyze  with  a  current  of  N.D100  =  0.02- 
0.04  ampere  and  2.6-2.7  volts.     The  cadmium  will  be 
deposited;  the  copper  will  remain  dissolved  (Jr.  An.  Ch., 
3,  385;  Z.  f.  ph.  Ch.,  12,  122).    Rimbach  (Z.  f.  a.  Ch.,  37, 


I4O  ELECTRO-CHEMICAL    ANALYSIS. 

288)  has  tried  this  separation  with  marked  success  in 
the  analysis  of  aluminium-cadmium-tin  alloys  con- 
taining copper  as  impurity.  In  case  the  nitrate  of  cad- 
mium is  used  it  will  be  necessary  to  increase  the  current 
to  N.D100  =  0.4  ampere. 

10.  From  Gold.     This  separation  is  not  recorded.     It  is 
probable  that  it  can  be  executed  in  a  hot  alkaline  cy- 
anide solution. 

11.  From  Iron:— 

(a)  In  sulphuric  acid  solution.     Follow  the   directions 
given  in  a  under  cadmium  from  aluminium,  p.  137. 
It  may  be  observed  that  this  is  the  procedure  used, 
too,  in  separating  cadmium  from  chromium. 

(b)  In  phosphoric  acid  solution.     Again  the  conditions 
noticed  in  b  under  cadmium  from  aluminium    (p. 
138)  will  prove  to  be  very  satisfactory  in  this  par- 
ticular case. 

(c)  In  potassium  cyanide  solution.  Dissolve  a  mixture  of 
cadmium  and  ferrous  sulphates  in  100  c.c.  of  water, 
previously  acidulated  with  a  few  drops  of  dilute  sul- 
phuric acid,  introduce  2  to  3  grams  of  pure  potassium 
cyanide,  and  heat  gently  until  perfect  solution  en- 
sues.    If  considerable  time  elapses  before  the  liquid 
becomes  yellow  in  color,  add  a  few  drops  of  caustic 
potash.     Dilute  the  liquid  to  200  c.c.  and  electrolyze 
the  cold  solution  with  a  current  of  N.DIOO  =  0.05-0.1 
ampere.     The  deposit  of  cadmium  will  be  very  sat- 
isfactory (W.  Stortenbeker,  Z.  f.   Elektrochem.,  4, 
409). 

12.  From  Lead.     See  lead  from  cadmium,  p.  165. 

13.  From  Magnesium.     See  cadmium  from  barium,  etc., 
p.  139.     In  this  connection  it  may  be  stated  that  Rim- 
bach  (Z.  f.  a.  Ch.,  37,  289)  effected  this  separation  in  a 


SEPARATION    OF    METALS CADMIUM.  14! 

potassium  cyanide  solution.  The  precaution  is  made 
that  not  too  much  magnesia  be  present,  ammonium 
chloride  also  being  added  to  the  solution  to  hold  up  the 
magnesia.  The  current  strength  best  adapted  for  this 
separation  proved  to  be  N.D100  =  0.02-0.05  ampere. 
The  time  was  14  hours. 
14.  From  Manganese:— 

(a)  In  sulphuric  acid   solution.     As  manganese  sepa- 
rates readily  from  a  sulphate  solution  in  the  presence 
of  a  slight  excess  of  sulphuric  acid,  and  then,  too, 
upon  the  anode  (p.  95),  it  is  only  necessary  to  add 
from  2  to  3  c.c.  of  sulphuric  acid  (sp.  gr.  1.09)  to  the 
solution  of  the  metals,  dilute  to  125  c.c.,  and  electro- 
lyze  with  the  current  and  voltage  given  under  cad- 
mium from  aluminium,  a.     As  the  manganese  is  pre- 
cipitated upon  the  anode  as  dioxide,  make  the  larger 
dish  the  receiving  vessel  for  it;  further,  let  its  inner 
surface  be  roughened.     The  cadmium  is  deposited 
upon   the   cathode.     The  method  has  been  used  in 
this  laboratory  with  success. 

(b)  In  phosphoric  acid  solution.     An  idea  of  the  ac- 
curacy of  the  method  can  be  best  obtained  from  an 
actual  example.     The  conditions  also  for  work  will  be 
most  satisfactorily  learned  from  it.     Twenty  cubic 
centimetres  of  disodium  hydrogen  phosphate  (sp.  gr. 
1.0358)  and  3  c.c.  of  phosphoric  acid  (sp.  gr.  1.347) 
were  added  to  a  solution  containing  0.2399  gram  of 
cadmium  and  o.iooo  gram  of  manganese  and  the 
liquid  then  diluted  with  water  to  150  c.c.  and  electro- 
lyzed  at  the  ordinary  temperature  with  a  current  of 
i  ampere.     In  12  hours  0.2394  gram  of  cadmium  was 
precipitated.     There  was  not  the  slightest  deposition 
of  manganese  at  the  anode.     The  cadmium  deposit 


142  ELECTRO-CHEMICAL   ANALYSIS. 

was  crystalline  in  appearance.  It  was  washed  with 
hot  water.  Before  the  final  interruption,  the  cur- 
rent ought  to  be  increased  and  allowed  to  act  for  an 
hour.  The  acid  liquid  should  be  removed  with  a 
siphon  before  disconnecting  (Am.  Ch.  Jr.,  13,  206). 

15.  From  Mercury.     See  mercury  from  cadmium,  p.  149. 

16.  From    Molybdenum.     The  alkaline  cyanide  solution 
is  well  adapted  for  this  purpose.     Add  from  1.5  to   3 
grams  of  pure  potassium  cyanide,  dilute  to  200  c.c.,  and 
electrolyze  at  40°  C.  with  N.D100  =  0.03-0.04  ampere 
and   2.25-3.0  volts.      The  conditions  are  practically 
those  used  in  the  separation  of  cadmium  from  arsenic 
(Am.  Ch.  Jr.,  12,  428). 

17.  From  Nickel: — 

(a)  In  sulphuric  acid  solution.     To  the  solution  of  salts 
of  the  two  metals  add  2  to  3  c.c.  of  sulphuric  acid,  sp. 
gr.  1.09,  also  ammonium   sulphate,  and   electrolyze 
with  the  current  density  and  voltage  mentioned  in 
the  separation  of  cadmium  from  aluminium,  a,  p. 

137- 

(b)  In  phosphoric  acid  solution.     0.1827  gram  of  cad- 
mium and  0.1500  gram  of  nickel  (both  as  sulphates) 
were  precipitated  by  40  c.c.  of  disodium  hydrogen 
phosphate,  dissolved  in  3  c.c.  of  phosphoric  acid  (sp. 
gr.  1.347),  diluted  to  125  c.c.,  and  electrolyzed  at  the 
ordinary    temperature  with  N.D100  =  0.035    ampere 
and     2.5-3.0    volts.      The    precipitated    cadmium 
weighed  0.1820  gram.     It  was  washed  and  treated 
as  directed  upon  p.  69. 

(c)  In  alkaline  cyanide  solution.     The  solution  contain- 
ing the  double  cyanides  of  the  two  metals  is  well 
suited  for  this  separation,  but  it  is  absolutely  neces- 
sary to  have  a  little  free  sodium  hydroxide  present. 


SEPARATION    OF    METALS  -  CADMIUM.  143 

The  conditions  would  be  then  about  as  follows  :  Add 
to  the  solution  containing  0.17  23  gram  of  cadmium, 
and  o.  1600  gram  of  nickel,  2  grams  of  potassium  or 
sodium  hydroxide  and  3  grams  of  potassium  cyanide. 
Dilute  to  175  c.c.  and  electrolyze  at  40°  with  N.Dioo 
0.03-0.04  ampere  and  2.25-3.0  volts  (Am.  Ch.  Jr., 
12,  104;  Freudenberg,  2.  f.  ph.  Ch.,  12,  122). 
18.  From    Osmium.     The   only   recorded   separation   of 
these  two  metals  was  made  in  a  solution  of  potassium 
cyanide.     The  quantity  of  cyanide  was  1.5  grams  for 
0.3  gram  of  the  combined  metals.     The  dilution  of  the 
solution  equaled  170  c.c.;  it  was  electrolyzed  with  a 
current  of  N.D100  =  0.26  ampere  and  3-4  volts.    Time,  10 
hours;  temperature,  25°  (Jr.  An.  Ch.,  6,  87). 

An  electrolytic  separation  of   cadmium  from  plati- 
num and  palladium  is  not  known  (Am.  Ch.  Jr.,  12,  428; 


19.  From  Selenium.     This  separation  has  not  been  made. 

20.  From  Silver.     See  p.  169,  for  silver  from  cadmium. 

21.  From  Sodium.     See  the  separation  of  cadmium  from 
barium,  etc.,  p.  139. 

22.  From   Strontium.     See  the  separation  of  cadmium 
from  barium,  etc.,  p.  139. 

23.  From   Tellurium.     There   is   no    known   electrolytic 
separation. 

24.  From  Tin.     They  have  not  been  separated  electro- 
lytically. 

25.  From    Tungsten.     The    conditions    detailed    in    the 
separation  of  cadmium  from  arsenic  (p.  138)  and  under 
cadmium  from  molybdenum  (p.  142)  in  cyanide  solu- 
tion will  answer  here. 

26.  From  Uranium.     The  current  has  not  been  used  in 
their  separation. 


144  ELECTRO-CHEMICAL    ANALYSIS. 

27.  From  Vanadium.     They  have  not  been  separated  in 
the  electrolytic  way. 

28.  From  Zinc.      As  these  two  metals  are  so  frequently 
found  together,  both  in  natural  and  in  artificial  pro- 
ducts, it  is  not  surprising  that  electrolytic  methods 
have  been  sought  to  effect  their  separation  in  such  a 
manner  as  to  leave  no  doubt  in  the  mind  of   the  an- 
alyst.    They  should  be  and  indeed  are  preferable  to 
the  ordinary  gravimetric  procedures. 

The  first  method  proposed  and  published  was  that 
by  Yver  (B.  s.  Ch.  Paris,  34,  18).  It  is  based  upon 
the  fact  that  cadmium  separates  well— 

(a)  In  acetate  solutions.     Convert  the  metals  into  ace- 
tates by  the  addition  of  2   to   3   grams  of  sodium 
acetate  to  their  solution,  followed  by  several  drops  of 
free  acetic  acid.     Dilute  the  liquid  to  100  c.c.  and 
warm  to   70°  C.     Electrolyze  with    N.D100    =   o.io 
ampere  and  2.2  volts.     Time,  3-4  hours.     The  cad- 
mium (0.2  gram)  will  be  precipitated  in  a  crystalline 
form  and  free  from  zinc  (Am.  Ch.  Jr.,  8,  210). 

The  zinc  in  the  liquid  from  the  cadmium  deposit 
may  then  be  precipitated  by  the  method  of  Riche 
(p.  89). 

Mention  may  be  here  made  of  the  fact  that  Smith 
and  Knerr  (Am.  Ch.  Jr.,  8,  210)  electrolyzed  a  solu- 
tion of  cadmium  and  zinc  to  which  3-4  grams  of 
sodium  tartrate  and  tartaric  acid  had  been  added, 
with  a  current  of  N.D100=  0.3-0.4  ampere  and  2.25-3 
volts.  The  temperature  of  the  solution  was  60°. 

(b)  In  oxalic  acid  solution.     Eliasberg  (Z.  f.  a.  Ch.,  24, 
550)  proposed  this  method,  second  in  point  of  time, 
and  recommended  the  following  procedure :  Dissolve 
the  metallic  oxides  in  hydrochloric  acid,  evaporate 


SEPARATION    OF    METALS CADMIUM.  145 

their  solution  to  dryness,  take  up  the  residue  in 
water,  add  to  the  liquid  8  grams  of  potassium  oxalate 
(C2O4K2)  and  2  grams  of  ammonium  oxalate  ((NH4)2- 
C2O4),  dilute  to  120  c.c.,  heat  to  8o°-85°,  and  electro- 
lyze  with  N.D100  =  0.01-0.02  ampere  and  3  volts. 
The  cadmium  will  be  precipitated  free  from  zinc. 
See  also  Waller,  Z.  f.  Elektrochem.,  4,  241-247. 
From  6  to  7  hours  are  required  for  the  deposition  of 
0.2  gram  of  cadmium. 

(c)  In  sulphuric  acid  solution.     To  the  liquid  containing 
the  salts  of  the  two  metals  add  3  to  4  c.c.  of  a  concen- 
trated ammonium  sulphate  solution  and  follow  with 
2  to  3  c.c.  of  dilute  sulphuric  acid.     Dilute  to  100  c.c. 
and  electrolyze  with  N.D100  =  0.08  ampere  and  2.8- 
2.9  volts  (Neumann's  Elektrolyse,  p.  189). 

In  the  electro-chemical  laboratory  of  the  Univer- 
sity of  Munich  the  separation  of  cadmium  from  zinc 
is  in  a  certain  sense  a  combination  of  c  and  a.  For 
example,  sodium  hydroxide  is  added  to  the  sulphates 
of  the  metals  until  a  permanent  precipitate  is  formed ; 
this  is  then  dissolved  in  as  little  sulphuric  acid  as  pos- 
sible, the  solution  is  diluted  to  70  c.c.  and  the  cad- 
mium precipitated  by  a  current  of  N.D100=o.o7  am- 
pere. When  the  greater  portion  of  this  metal  has 
been  thrown  out  of  the  solution,  the  free  sulphuric 
acid  is  neutralized  with  sodium  hydroxide  and  2  to  3 
grams  of  sodium  acetate  are  introduced  into  the 
liquid,  which  is  heated  to  45°  and  electrolyzed  with  a 
current  of  N.D100  =  0.03  ampere  and  3.6  volts. 

(d)  In  phosphoric  acid  solution.     Total   dilution,    125 
c.c.;    cadmium,    0.1827    gram;    zinc,    0.1500    gram; 
disodium  hydrogen  phosphate  (sp.  gr.  1.038),  40  c.c. ; 
phosphoric  acid  (sp.  gr.  1.347),  3  c.c.;  N.D100  =  0.035 

13 


146  ELECTRO-CHEMICAL   ANALYSIS. 

ampere;  V  =  2.5-3.0.  Cadmium  found,  0.1820  gram. 
The  ordinary  temperature.  Time,  10  hours  (Am.  Ch. 
Jr,  12,329). 

(e)  In  potassium  cyanide  solution.  This  separation 
originated  in  this  laboratory  (Am.  Ch.  Jr.,  11,  352). 
Example :  0.2426  gram  of  cadmium  as  sulphate,  0.2000 
gram  of  zinc  as  sulphate;  4.5  grams  of  potassium  cy- 
anide; total  dilution,  200  c.c.  Ordinary  tempera- 
ture. N.D100  =  0.03  ampere;  volts  =2.8-3.2.  0.2429 
gram  of  cadmium  found. 

In  the  nitrate  the  zinc  may  be  precipitated  by  in- 
creasing the  current.  Freudenberg  used  this  method 
with  success,  applying  a  current  corresponding  to  an 
electromotive  force  of  2.6-2.7  volts. 


MERCURY. 

Experience  has  proved  that  this  metal  is  most  accu- 
rately determined,  and  most  satisfactorily  separated  from 
the  metals  usually  found  with  it  by  the  use  of  electrolytic 
methods  which  in  this  instance  are  preferable  in  every 
particular  to  the  ordinary  gravimetric  courses;  hence 
all  the  known  separations  in  the  electrolytic  way  will  be 
given,  in  the  paragraphs  which  follow,  with  such  detail 
that  no  doubt  need  remain  as  to  the  final  results. 

1.  From  Aluminium:— 

(a)  In  nitric  acid  solution  (p.  121).     Add  3  c.c.  of  con- 
centrated nitric  acid  to  the  solution  of  the  two  salts, 
dilute  to  125  c.c.,  heat  to  70°  C.,  and  electrolyze  with 
N.D100   =  0.06  ampere  and   2  volts.     Time,  2  hours. 
The  solution  in  the  dish  must  be  siphoned  off  before 
the  interruption  of  the  current. 

(b)  In  sulphuric  acid  solution  (p.  121).     Add  i  c.c.  of 


SEPARATION    OF    METALS MERCURY.  147 

sulphuric  acid  to  the  solution  of  the  salts;  dilute  to 
125  c.c. ;    heat  to  65°  and  electrolyze  with  N.D100  = 
0.4-0.6  ampere  and  3.50  volts.     The  mercury  (o.  1500 
gram)  will  be  precipitated  in  an  hour.     Wash  it  with 
cold  water  and  proceed  as  directed  on  p.  74. 

2.  From    Antimony.     Add  to   the    solution,   containing 
about  equal  amounts  of  the  two  metals,  5  grams  of 
tartaric  acid  and  15-20  c.c.  of  ammonia  water  (10  per 
cent.);  dilute  to  175  c.c.  and  electrolyze  with  N.D100  = 
0.015-0.085   ampere    and    2.2-3.5   volts.      The    tem- 
perature   should    be    50°.      About    6    hours    will    be 
required    for     the     precipitation    (J.    Am.     Ch.      S., 
15,  205).     The  antimony  must  exist  in  solution  as  an 
antimonic  compound.     The  method  was  first  worked 
out  by  Schmucker  (loc.  cit.)  and  was  later  successfully 
confirmed  by  Freudenberg  in  his  study  of  the  differences 
in  potential  (Z.  f.  ph.  Ch.,  12,  112),  when  he  employed 
an  electromotive  force  of  1.6-1.7  volts.     Mercury  used, 
0.2362  gram;  mercury  found,  0.2356  gram;  antimony 
present,   0.2600  gram. 

The  liquid  from  the  deposit  of  mercury,  after  acidula- 
tion,  may  be  precipitated  with  hydrogen  sulphide  and 
the  resulting  sulphide  be  dissolved  in  sodium  sulphide 
and  treated  as  described  on  p.  115  for  the  determination 
of  the  antimony. 

3.  From  Arsenic:— 

(a)  In  nitric  acid  solution.     The  solution  of  the  metals 
should  contain  a  few  cubic  centimetres  of  free  nitric 
acid  and  then  be  acted  upon  with  an  electromotive 
force  of  1.7-1.8  volts:  Mercury  taken,  0.2380  gram; 
mercury  found,  0.2380  gram;  arsenic  present,  0.2516 
gram  (Freudenberg,  Z.  f.  ph.  Ch.,  12,  in). 

(b)  In  potassium  cyanide  solution.     Add   3   grams  of 


148  ELECTRO-CHEMICAL    ANALYSIS. 

pure  potassium  cyanide  to  the  liquid  containing  0.5 
gram  of  combined  metals,  dilute  to  200  c.c.,  and  elec- 
trolyze  with  N.D100=  0.015  ampere  and  2.2-3.5  volts 
for  5  hours  at  65°  (Am.  Ch.  Jr.,  12,  428).  It  is 
immaterial  whether  the  arsenic  is  present  as  an 
arsenite  or  arsenate. 

(c)  In  alkaline  sulphide  solution  (p.  74).  An  example 
will  best  illustrate  the  method:  To  the  solution  of 
mercury  add  25  c.c.  of  sodium  sulphide  (sp.  gr,  1.19), 
dilute  with  water  to  125  c.c.,  heat  to  70°  C.,  and 
electrolyze  with  a  current  of  N.D100=  o.  n  ampere 
and  2.5  volts.  The  time  for  precipitation  is  usually 
5  hours.  See  Jr.  Fr.  Ins.,  1891. 

4.  From  Barium,  Strontium,  Calcium,  Magnesium,  and  the 
Alkali    Metals.     Use   method   a   under   mercury  from 
aluminium  (p.  146)  for  this  purpose. 

5.  From  Bismuth.     The  statements  with  reference  to  the 
separation  of  these  two  metals  are  contradictory.     The 
experiments  conducted  in  this  laboratory  (Jr.  An.  Ch., 
7,  252)  showed  that  the  metals  were  coprecipitated  from 
a  nitric  acid  solution,  as  one  from  many  examples  will 
illustrate:    The    solution    contained    0.1132    gram    of 
mercury  and  0.07 1 6  gram  of  bismuth.     Ten  cubic  centi- 
metres of  nitric  acid  of  specific  gravity  1.2  were  added 
and  the  liquid  diluted  with  water  to  200  c.c.  and  elec- 
trolyzed  with  a  current  of    N.D100   ==  0.04  ampere  and 
1.6  volts. 

The  precipitation  of  the  metals  was  complete,  but 
the  mercury  contained  bismuth.  This  was  one  of  eight 
trials  which  resulted  similarly.  They  were  made  to 
disprove  a  statement  which  had  appeared  repeatedly  in 
three  editions  of  Classen's  Quantitative  Analyse  durch 
Elektrolyse  (p.  147,  2d  ed.),  despite  the  fact  that  the 


SEPARATION    OF    METALS  —  MERCURY.  149 

same  writer  had  declared  previously  (Ber.,  19,  325): 
"  Bismuth  cannot  be  separated  from  mercury  in  this 
manner.  Both  metals  are  precipitated  simultaneously 
from  an  acid  solution." 

After  this  study  had  been  made,  Freudenberg  (Z.  f. 
ph.  Ch.,  12,  in),  by  adherence  to  the  idea  of  the  differ- 
ences in  potential,  gave  results  which  would  indicate  a 
complete  separation;  a  few  cubic  centimetres  of  nitric 
acid,  of  sp.  gr.  1.2,  and  2-4  grams  of  ammonium  nitrate 
are  added  to  the  nitrate  solution  of  the  two  metals  and 
the  electrolysis  conducted  with  a  potential  of  1.3  volts. 
Mercury  used,  0.2380  gram;  mercury  found,  0.2376 
gram;  bismuth  present,  0.2694  gram.  As  Neumann 
(Elektrolyse,  p.  181)  remarks,  the  possible  current 
strength  is  exceedingly  low,  hence  a  long  time  is  re- 
quired for  the  precipitation  of  the  mercury. 

While  the  writer  has  never  tested  the  recommenda- 
tion of  Freudenberg,  his  experience  gathered  from  nu- 
merous attempts  on  the  part  of  his  students  inclines 
him  to  say  that  the  procedure  is  worthy  of  further 
study  at  least. 
6.  From  Cadmium:— 

(a)  In  acid  solution.  The  nitric  acid  and  sulphuric 
acid  solutions  lend  themselves  quite  well  to  this 
separation.  The  proper  conditions  for  the  obtain- 
ment  of  satisfactory  results  are  given  in  the  section 
on  mercury  from  aluminium,  paragraphs  a  and  b  (p. 


(b)  In  alkaline  cyanide  solution.  The  solution  con- 
tained 0.1182  gram  of  mercury  and  0.2206  gram  of 
cadmium.  Two  and  one-half  grams  of  pure  potas- 
sium cyanide  were  added,  and  the  liquid  was 
then  diluted  with  water  to  125  c.c.,  heated  to  65°, 


I5O  ELECTRO-CHEMICAL    ANALYSIS. 

and  acted  upon  with  a  current  of  N.D100  ••  =  0.018 
ampere  and  1.7  volts.  The  precipitation  was  com- 
plete in  7  hours  at  the  ordinary  temperature  (J.  Am. 
Ch.  $.,  21,  919;  also  17,  612). 

7.  From  Calcium.     See  the  separation  of  mercury  from 
barium  (p.  148). 

8.  From  Chromium.     The  methods  recommended  for  the 
separation  of  mercury  from  aluminium,  pp.   146,   147, 
will  answer  for  this  particular  purpose. 

9.  From  Cobalt  :— 

(a)  In  acid  solutions.     See  p.  146,  under  mercury  from 
aluminium. 

(b)  In   alkaline   cyanide   solution.     The   solution   con- 
tained o.i  216  gram  of  mercury  and  o.iooo  gram  of 
cobalt.     The  liquid  was  diluted  to  100  c.c.;  2  grams 
of  potassium  cyanide  were  added  to  it  and  the  liquid, 
then  heated  to  65°,  was  electrolyzed  with    N.D100  = 
0.025-0.03  ampere  and  2.06-2.7  volts  for  5  hours. 
The  mercury  found  equaled  0.1213  gram  and  0.1217 
gram.     Too    much   potassium   cyanide   exercises    a 
retarding  influence  on  the  precipitation  of  the  mer- 
cury (J.  Am.  Ch.  S.,  21,  918;  Am.  Ch.  Jr.,  12,  104). 

10.  From  Copper:— 

(a)  In  nitric  acid  solution.  Freudenberg  (Z.  f.  ph.  Ch., 
12,  in),  with  attention  to  voltage  alone,  separates 
these  metals  as  follows:  To  their  solution  (the  ni- 
trates) add  several  cubic  centimetres  of  nitric  acid  (sp. 
gr.  1.2)  and  2  to  4  grams  of  ammonium  nitrate,  after 
which  electrolyze  with  a  current  having  a  pressure  of 
1.3  volts.  Mercury  present,  0.2380  gram;  copper 
present,  0.1356  gram;  mercury  found,  0.2377  gram; 
copper  found,  0.1358  gram.  The  separation  was 
made  during  the  night. 


SEPARATION    OF    METALS MERCURY.  151 

(b)  In  alkaline  cyanide  solution.  It  was  in  a  solution  of 
the  double  cyanides  of  these  metals  that  they  were 
first  separated  successfully  in  the  electrolytic  way 
(Am.  Ch.  Jr.,  11,  264).  At  the  time  it  was  thought 
that  the  separation  could  not  be  regarded  as  yielding 
trustworthy  results  when  the  copper  exceeded  20  per 
cent.,  but  about  two  years  subsequently  it  was 
shown  (Jr.  An.  Ch.,  5,  489)  that  by  careful  adjust- 
ment of  the  current  strength  the  quantity  of  copper 
could  not  only  equal,  but  exceed,  that  of  the  mercury 
almost  indefinitely  (Spare  and  Smith,  J.  Am.  Ch.  S., 
23,  579).  The  time,  however,  was  still  an  important 
factor,  and  it  was  not  reduced  by  Freudenberg,  who 
electrolyzed  the  double  cyanides  with  a  pressure  of 
2.5  volts,  in  the  presence  of  2  to  4  grams  of  potassium 
cyanide  (Z.  f.  ph.  Ch.,  12,  113).  The  reduction  of 
this  factor  was  made  in  1894  (J.  Am.  Ch.  S.,  16,  42) 
by  gently  warming  the  electrolyte.  It  then  became 
possible  to  fully  precipitate  the  mercury  in  three  and 
one-half  hours.  Since  then  the  separation  has  been  re- 
peatedly made  both  with  mercury  and  copper  (J.  Am. 
Ch.  S.,  21,  917),  and  with  mercury,  copper,  cadmium, 
zinc,  and  nickel  simultaneously  present.  The  follow- 
ing conditions  will  prove  satisfactory  for  this  separa- 
tion: Mercury  present,  o.  1 2 1 6  gram ;  copper  present, 
equal  amount;  total  dilution,  125  c.c.;  potassium 
cyanide,  2-3  grams;  temperature,  65°;  time,  2^-3 
hours.  Mercury  found,  0.1215  gram  (Revay,  £.  f. 
Elektrochem.,  4,  313). 

11.  From   Gold.     This   separation  has   not   been   made. 
See  Z.  f.  ph.  Ch.,  12,  113. 

12.  From  Iron: — 

(a)  In  nitric  acid  solution.  Use  the  conditions  indi- 
cated under  a,  mercury  from  aluminium  (p.  146). 


152  ELECTRO-CHEMICAL    ANALYSIS. 

(b)  In  sulphuric  acid  solution.     See  b  under  mercury 
from  aluminium. 

(c)  In  alkaline  cyanide  solution.     Dissolve  ferrous  am- 
monium sulphate  in  water;  conduct  sulphur  dioxide 
through  it  to  reduce  any  ferric  salt  which  may  be 
present,   nearly  neutralize  the  excess  of  acid  with 
sodium  carbonate,  mix  with  the  solution  of  the  sil- 
ver salt,  and  add  from  2.5  to  4  grams  of  potassium 
cyanide  for  0.2-0.4  gram  of   the  combined   metals; 
then  electrolyze  with  N.D100  =  0.02-0.05  ampere  and 
2.5  volts,  with  a  temperature  of  70°.     The  total  dilu- 
tion should  equal  125  c.c.     Time,  3-4  hours  (J.  Am. 
Ch.  S.,  21,  920). 

13.  From    Lead.     To   the  solution,   containing  the  two 
metals,  add  from  25  to  30  c.c.  of  nitric  acid  (sp.  gr.  1.3), 
dilute  to   175  c.c.  with  water,  and  electrolyze  with  a 
current  of  N.D100  =  0.13  to  0.18  ampere  and   2   volts, 
at  30°  for  4  hours.     It  will,  of  course,  be  understood 
that  the  lead  is  deposited  as  dioxide  upon  the  anode 
while  the  mercury  is    simultaneously  precipitated  in 
the  cathode.     Use  a  dish  as  anode  (Smith  and  Mover, 
Jr.  An.  Ch.,  7,  252;  Z.  f.  anorg.  Ch.,  4,  267;    Heiden- 
reich,  Ber.,  29,  1585;  2.  f.  Elektrochem.,  3,  151). 

14.  From   Magnesium.     See  the  separation  of  mercury 
from  barium,  etc.,  p.  148. 

15.  From  Manganese :— 

(a)  In  nitric  acid  solution.  See  the  conditions  under 
which  manganese  is  precipitated  as  dioxide  (p.  95). 
The  mercury  separates  at  the  cathode. 

(6)  In  sulphuric  acid  solution.  The  conditions  which 
should  be  observed  in  depositing  manganese  from  a 
solution  containing  free  sulphuric  acid  will  answer 


SEPARATION    OF    METALS MERCURY.  153 

in  this  particular  separation  (p.  96).  The  larger 
dish  must,  of  course,  be  made  the  anode.  The 
quantities  of  the  two  metals  must  not  be  too  large. 

16.  From    Molybdenum.     The   separation  is   readily   ef- 
fected in  an  alkaline  cyanide  solution,  using  the  condi- 
tions prescribed  under  b  in  the  separation  of  mercury 
from  arsenic  (p.  147). 

17.  From  Nickel:— 

(a)  In  nitric  acid  solution.     Follow  the  conditions  given 
under  a  in  the  separation  of  mercury  from  aluminium, 
p.  146. 

(b)  In  sulphuric  acid  solution.     Reproduce  the  condi- 
tions of  b  in  the  separation  of  mercury  from  alumin- 
ium, p.  146. 

(c)  In  alkaline  cyanide  solution.     An  example  will  illus- 
trate:   Mercury  present,   0.1216  gram;  nickel  pres- 
ent, 0.1500  gram;  potassium  cyanide,  2-2.5  grams; 
total  dilution,  125  c.c.;  N.D100=  0.04  ampere;    volts 

1.7-2.2;  temperature,  65°;  time,  4  hours.  The 
mercury  found  equaled  0.1213  gram  (J.  Am.  Ch.  $., 
21,918;  Am.  Ch.  Jr.,  12,  104). 

18.  From  Osmium.     Follow  the  directions  for  the  sepa- 
ration of  mercury  from  arsenic  in  an  alkaline  cyanide 
solution,  p.  147.     In  this  separation  the  quantity  of  al- 
kaline cyanide  should  not  exceed    1.5   grams  for  0.2 
gram  of  metal  (Am.  Ch.  Jr.,  12,  428;   13,  417;  Jr.  An. 
Ch.,  6,  87). 

19.  From  Palladium.     Let  the  conditions  be  the  same  as 
those  given  for  the  separation  of  mercury  from  platinum 
(see  below)  (Am.  Ch.  Jr.,  12,  428). 

20.  From  Platinum.     Example:  Mercury  present,  0.1373 
gram;  platinum  present,  o.  1000  gram;  total  dilution, 
125   c.c.;  potassium  cyanide,  3  grams;  N.D100  ==  0.04- 

14 


154  ELECTRO-CHEMICAL   ANALYSIS. 

0.05  ampere;  V  =  2.1;  temperature,  65°-75°;  time,  4 
hours.  The  mercury  found  equaled  0.1372  gram  (Am. 
Ch.  Jr.,  13,  417;  J.  Am.  Ch.  S.,  21,  920). 

21.  From   Potassium.     See  mercury  from  barium,   etc., 
p.  148. 

22.  From  Silver.     These  metals  cannot  be  separated  elec- 
trolytically  either  in  an  acid  or  alkaline  cyanide  solu- 
tion.    Classen  precipitates  them  together,   and  after 
ascertaining  their  combined  weight  expels  the  mercury 
by  ignition  and  weighs  the  residual  silver. 

23.  From  Sodium.     See  barium,  p.  148. 

24.  From  Strontium.      See  mercury  from  calcium,   etc., 
p.  148. 

25.  From   Tellurium.     There   is  no  known    electrolytic 
separation. 

26.  From  Tin:— 

(a)  In  alkaline  sulphide  solution.     The  conditions  men- 
tioned under  mercury  (p.  74)  will  answer  perfectly 
for  this  separation  (Jr.  Fr.  Ins.,  1891).     To  change 
the  sodium  sulpho-salt  in  the  filtrate  into  ammo- 
nium sulphostannate  consult  p.  113. 

(b)  In  ammoniacal  tartrate  solution.     A  solution  of  the 
two  metals  was  made  by  adding  mercuric  chloride  to 
tartaric  acid,  followed  by  ammonia  water  and  then 
diluting  with  water.     This  solution  was  then  mixed 
with  the  tin  salt  solution  and  the  combined  liquids 
electrolyzed    with  a  current  showing  a    pressure  of 
from  1.6-1.7  volts.     (See  the  separation  of  mercury 
from  antimony  in  tartrate  solution,  p.  147 ;  also  J.  Am. 
Ch.  S.,  15,  p.  204.) 

It  may  be  of  interest  to  state  that  the  conditions 
given  for  the  separation  of  mercury  from  an- 
timony (p.  147),  and  those  just  employed  above 


SEPARATION  OF  METALS MERCURY.  155 

for  the  separation  of  mercury  from  tin  have 
been  successfully  applied  by  Schmucker  (J. 
Am.  Ch.  $.,  15,  204)  for  the  electrolytic  sep- 
aration of  mercury  from  a  solution  containing 
arsenic,  antimony,  and  tin,  the  only  change  being  in 
the  addition  of  an  increased  amount  of  tartaric  acid 
and  ammonia  water.  Example:  Mercury,  0.0933 
gram;  arsenic,  0.1009  gram;  antimony,  0.1031  gram; 
tin,  o.  1000  gram;  tartaric  acid,  8  grams;  ammonia, 
30  c.c.;  dilution,  175  c.c.;  N.D100  =  0.05  ampere; 
volts  1.7.  The  precipitation  made  at  60°  was 
complete  in  6  hours. 

27.  From   Tungsten.     Use   conditions   corresponding   to 
those   employed   in   the   separation   of   mercury  from 
arsenic  in  an  alkaline  cyanide  solution  (p.  147). 

28.  From    Uranium.     There  is  no  recorded  electrolytic 
separation  of  these  metals,  but  it  is  quite  probable  that 
methods  a  and  b,  under  mercury  from  aluminium  (p. 
146),  would  be  applicable  in  this  case. 

29.  From  Vanadium.     They  have  not  been  separated  by 
the  current. 

30.  From  Zinc:— 

(a)  In  acid  solutions  (nitric  or  sulphuric)  the  conditions 
mentioned  under  a  and  b,  in  the  separation  of  mer- 
cury from  aluminium,  will  prove  perfectly  satisfac- 
tory (p.  146). 

(b)  In  alkaline  cyanide  solution.     This  separation  has 
been  made  repeatedly  with  excellent  success,  so  that 
perhaps  an  actual  example  will  give  all  the  data 
necessary  to  guide  others  in  making  the  separation : 
Mercury  present,  0.1158  gram;  zinc  present,  o.  1000 

.     gram;  potassium  cyanide,  1.5  to  2  grams;  dilution, 
125  c.c.;  N.D100  =  0.025-0.05  ampere;  V    =  2.5  to  3; 


156  ELECTRO-CHEMICAL    ANALYSIS. 

time,  4  hours;  temperature,  60°.  Mercury  found, 
o.i  1 55  gram  (J.  Am.  Ch.  S.,  21,  919;  Jr.  Fr.  Ins.,  1889). 
(c)  In  phosphoric  acid  solution.  An  example  from 
many  results  will  show  the  conditions  which  should 
be  pursued  in  conducting  the  separation  in  a  solution 
such  as  just  indicated:  25  c.c.  of  mercuric  chloride 

=  0.1159  gram  of  metal;  25  c.c.  of  zinc  sulphate  = 
o.i oio  gram  of  metal;  60  c.c.  of  disodium  hydrogen 
phosphate  (1.038  sp.  gr.);  loc.c.  of  phosphoric  acid 
(1.347  sp.  gr-);  total  dilution,  175  c.c.;  temperature, 
60°;  N.  100  ==  o.oi  ampere;  V  1.5;  time,  4-5 
hours.  Mercury  found,  0.1163  gram  (J.  Am.  Ch. 
S.,  21,  1006). 


BISMUTH. 

The  separations  of  this  metal  from  other  metals  in  the 
electrolytic  way  are  not  numerous,  but  they  are,  notwith- 
standing, of  decided  help  to  the  analyst,  and  therefore 
will  be  here  presented  in  such  detail  as  is  known. 

1.  From  Aluminium.     The  conditions  given  under  bis- 
muth for  its  determination  in  a  nitric  (p.  76)  or  sul- 
phuric acid  (p.  76)  solution  can  be  here  used  for  its 
separation  from  aluminium.     Its  precipitation  as  an 
amalgam  (p.  75)  is  well  adapted  for  this  purpose. 

2.  From  Antimony.     To  the  solution  containing  the  two 
metals  add  5  grams  of  tartaric  acid,  15  c.c.  of  ammo- 
nium hydroxide,  dilute  to  175  c.c.  with  water,  and  elec- 
trolyze  with  a  current  of  N.D100  =  0.022   ampere  and 
1.8  volts  at  50°  for  6  hours   (J.  Am.  Ch.  S.,  15,  203). 

3.  From  Arsenic.     The  course  just  outlined  for  the  separa- 
tion of  bismuth   from  antimony   will   answer  in  this 


SEPARATION  OF  METALS BISMUTH.  157 

case  (J.  Am.  Ch.  S.,  15,  202).  Neumann  (Elektro- 
lyse,  p.  185)  states  that  the  two  metals,  if  in  sulphate 
solution,  can  be  separated  with  a  current  having  an  E. 
M.  F.  of  1.9  volts. 

4.  From  Barium.     The  conditions  for  the  precipitation  of 
bismuth  from  nitric  acid  solution  (p.  76)  will  answer  for 
this  separation. 

5.  From  Cadmium.     This  separation  may  be  conducted 
in  the  presence  of  free  nitric  acid  (p.  76),  by  the  amal- 
gam method  (p.  75),  or  in  a  sulphuric  acid   solution. 
If  using  the  last  electrolyte,  proceed  as  follows:  Dis- 
solve o.  1500  gram  of  cadmium  metal  in  2  c.c.  of  concen- 
trated sulphuric  acid  (sp.  gr.  1.84)  and  to  this  solution 
add  another  of  0.15  gram  of  bismuth  and  i  c.c.  of  con- 
centrated nitric  acid,  i  gram  of  potassium  sulphate,  and 
dilute  with  water  to  150  c.c.,  heat  to  50°,  and  electro- 
lyze  with  a  current  of    N.D100   ==  0.025  ampere  and  2 
volts.     Time,  8  hours.     The  bismuth  will  be  deposited 
in  a  bright,  metallic  form  (Kammerer). 

6.  From  Calcium.     The  conditions  given  on  pp.   75-78 
for  the  determination  of  bismuth  may  be  relied  upon  in 
making  this  separation. 

7.  From  Chromium.     Use  a  nitric  acid  solution  (p.  76),  or 
adopt  the  method  given  in  the  following  paragraph : — 

To  a  solution  of  bismuth  containing  0.1500  gram  of 
metal  and  i  c.c.  of  nitric  acid  (sp.  gr.  1.42)  add  0.5  gram 
of  potassium  sulphate,  2  c.c.  of  sulphuric  acid  (sp.  gr. 
1.84),  and  a  quantity  of  chrome  alum  equivalent  to 
o.  1 500  gram  of  chromium.  Dilute  to  1 50  c.c.  with  water 
and  electrolyze  with  a  current  strength  of  N.D]00  = 
0.025  ampere  and  2  volts,  the  temperature  being  main- 
tained at  50°  C.  After  8  hours  the  deposition  will  be 
complete  and  the  bismuth  will  be  free  from  chromium. 


158 


ELECTRO-CHEMICAL    ANALYSIS. 
RESULTS. 


E* 

x  • 

S 

D 

D  H 

u 

s  . 

o 

u 

§ 

w 

b 

0  „; 

D  Z 

s 

^ 

D  Q 

x  n 

s 

Q* 

S 

w  Q 

1* 

^  O 

o 

<  0, 

5< 

D 

0 

£J  7 

«'* 

X 

O  D 

^3 

c. 

^i 

> 

f-<3 

o 

OuC/2 

Cfl 

W 

t_i 

Grm. 

Grm. 

Grm. 

Grm. 

C.c. 

C.c. 

Hours. 

0(, 

AMP. 

o.  1434 

0.1430 

0.1500 

0-5 

2 

2OO 

9 

50 

0.03 

2 

Gauze. 

o.  1434 

0.1428 

o.  150 

0-5 

2 

150 

9 

50 

0.025 

2 

Basket. 

0.1434 

0.1434 

0.1500 

o-,S 

2 

2OO 

8  ^ 

So 

0.025 

2 

Gauze. 

0.1434 

o  1428 

0.1500 

0-5 

2 

150 

8^ 

50 

O.O2 

2 

Basket. 

o.  1434 

0.1430 

0.1500 

0.5 

2 

150 

8X 

50 

O.O2 

2 

Spiral. 

0.1434 

0.1429 

0.1500 

0-5 

2 

150 

9 

0.025 

2 

The  chromium  salt  seems  to  exert  a  beneficial  influ- 
ence on  the  character  of  the  deposit.  Much  of  the 
chromium,  during  the  electrolysis,  is  oxidized  to  chromic 
acid.  Especially  is  this  true  when  gauze  electrodes  are 
used  (Kammerer). 

8.  From  Cobalt.     Proceed  as  in  the  separation  from  alu- 
minium (p.  156),  or  from  chromium  (above). 

9.  From  Copper.     In  a  nitric  acid  solution  copper  and  bis- 
muth cannot  be  separated  electrolytically.     This  state- 
ment has  been  the  subject  of  considerable  controversy 
in  past  years  (Z.  f.  anorg.  Ch.,  3,  415;  4,  234;  5,  197; 
6,  43;  Z.  f.  ph.  Ch.,  12,  117),  so  that  all  that  remains  to 
chemists  is  the  suggestion  made  in  the  Am.  Ch.  Jr.,  12, 
428 — viz.,  add  from  3  to  4  grams  of  citric  acid  to  the 
bismuth  solution,  supersaturate  the  latter  with  sodium 
hydroxide,  and  into  this  mixture  pour  the  copper  salt 
solution,  containing  a  slight  excess  of  potassium  cyan- 
ide, and  electrolyze  at  the  ordinary  temperature  with  a 
current  of  N.D100   ==  0.05  ampere  and    2.7  volts.     In  9 
hours  the  bismuth  will  be  fully  precipitated  and  will 
not  contain  any  copper. 


SEPARATION  OF  METALS BISMUTH.  159 

10.  From     Gold.      There     is    no     recorded     electrolytic 
separation  of  these  metals. 

11.  From  Iron.     The  acid  solutions  and  conditions,  given 
on  pp.  75-78,  will  answer  in  this  case.     It  may  be  re- 
marked here  that  the  deposition  of  bismuth  from  sul- 
phuric acid  solutions  containing  iron  is  attended  with 
considerable  difficulty.     The  iron  present  seems  to  ex- 
ert an  influence  on  the  bismuth,  tending  to  hold  it  in 
solution  and  prevent  its  deposition  by  the  current. 
Especially  is  this  true  when  the  salt  used  is  a  ferric  salt. 
This  tendency  of  bismuth  to  be  held  in  solution  is  shown 
even  in  a  more  marked  degree  when  the  liquid  contains 
besides  ferric  alum  an  equal  quantity  of  chrome  alum. 
A  current  of  o.  10  ampere  will  often  not  cause  the  slight- 
est precipitation  of  bismuth.     It  was  thought  that  this 
behavior  of  bismuth  could  be  used  to  separate  other 
metals  from  it.    It  was  hoped  that  the  bismuth  would  be 
held  back  by  the  iron  and  chrome  alums  and  such 
metals  as  mercury,  copper,  and  silver  be  deposited  from 
the  solution.     These  hopes  were  not  realized.     As  soon 
as  another  metal  is  introduced  the  condition  of  affairs 
is  changed,  and  both  the  metal  and  the  bismuth  are 
precipitated.     Deposits   of  silver,   however,   were   ob- 
tained containing  but  very  little  co-precipitated  bis- 
muth.    Further  investigation  in  this  direction  might 
lead  to  some  very  interesting  and  valuable  results. 

The  best  conditions  for  the  separation  of  bismuth 
from  iron  were  found  to  be  as  follows :  To  the  bismuth 
solution  containing  0.15  gram  of  bismuth  and  i  c.c.  of 
concentrated  nitric  acid,  add  2  c.c.  of  sulphuric  acid  (sp. 
gr.  1.84),  0.5  gram  of  potassium  sulphate,  and  a  quan- 
tity of  ferrous  sulphate  or  ammonium  ferric  alum  equiv- 
alent to  0.15  gram  of  iron.  This  solution  should  be 


i6o 


ELECTRO-CHEMICAL    ANALYSIS. 


diluted  to  150  c.c.  and  electrolyzed  at  a  temperature  of 
45°  C.  If  a  ferrous  salt  is  used,  the  current  strength 
should  be  0.03  ampere,  but  if  a  ferric  salt  is  in  solution, 
a  higher  current  strength  should  be  employed, — 0.05 
ampere, — the  voltage  in  both  cases  being  2.0.  In  eight 
hours  the  deposition  will  be  complete.  The  precipi- 
tated bismuth  is  free  from  iron  (Kammerer). 

In  several  cases  the  separation  was  made  in  the  pres- 
ence of  urea  nitrate,  but  its  addition  was  no  advantage. 

RESULTS. 


u 

SM 

z 

u 

, 

fc 

£a 

D  Z 

z  2 

25 

«< 

o 

S.I 

Is  f     * 

w« 

i    {2 

°  a 

v  a 

i< 

|f 

~H 

S| 

^  X 

<  0, 

H  -: 
0  0 

E> 

J 

Q 

D 
(fl 

rt 

h 

I1 

P 

Grm. 

Grm. 

Grm. 

Grm. 

Grm. 

C.c. 

C.c.       Hours. 

oC 

Amp. 

o.  1434 

0.  1429 

0.1500* 

.    . 

0-5 

ISO 

2 

8/4 

50 

0.025  '-5 

Spiral. 

0.1431 

o.  1500* 

.    . 

0.6 

150 

2 

7/^2 

45 

003      2 

" 

0.1435 

0.1500*      .     . 

0-5 

150 

2 

24 

45 

0.03       2 

" 

0.1430 

o.  1  500* 

0-5 

150 

2 

24 

45 

0.03       1.7 

Basket. 

o.  1395  jo.  1394 

0.1500* 

0-5 

O.2 

150 

2 

45 

0.035    2 

*' 

0.1400 

o.  1  500* 

o-5 

O.2 

2 

8 

5° 

0.035    2 

Spiral. 

0.1393 

0.1500* 

o-5 

O.2 

2OO 

2 

0 

45 

0.05       2 

Gauze. 

0.1397 

o.i  5  oof 

0-5 

150 

2 

9 

45 

007       2 

Spiral. 

0.1395 

0.1500!     .    . 

I 

!5° 

2 

9 

45 

O.O6       2 

'  ' 

0.1394 

0.1500]- 

I 

2OO 

2 

8 

45 

O.O6       2 

Gauze. 

0.1395 

0.1500} 

3-o 

0-5 

150 

2 

9 

45 

0.035    2 

Spiral. 

*  Ferrous  sulphate. 

•(•  Ferric  ammonium  sulphate. 

12.  From  Lead.  Experiments  made  in  this  laboratory 
(Jr.  An.  Ch.,  7,  252)  have  demonstrated  that  the  gener- 
ally accepted  statement  that  the  metals  could  be  separ- 
ated in  the  presence  of  free  nitric  acid  is  not  correct. 
The  lead  dioxide  invariably  contained  bismuth.  We 
are,  therefore,  for  the  present  at  least,  without  an 
electrolytic  method  for  their  separation. 


SEPARATION  OF  METALS BISMUTH.  l6l 

13.  From  Magnesium.     The  acid  solutions  and  conditions 
given  for  the  separation  of  bismuth  from  aluminium 
(p.  156)  will  serve  to  effect  this  particular  separation. 

14.  From  Manganese.     To  the  bismuth  solution  contain- 
ing o.  1500  gram  of  metal  and  i  c.c.  of  nitric  acid  (sp.  gr. 
1.42)  add  3  c.c.  of  sulphuric  acid  (sp.  gr.  1.84),  0.5  gram 
of  potassium  sulphate,  and  a  quantity  of  manganous  sul- 
phate equivalent  to  0.1500  gram  of  manganese.     Dilute 
this  solution    to   150  c.c.  with  water   and    electrolyze 
with  a  current  of  N.D100  =  0.025  ampere  and  2  volts, 
keeping  the  temperature  at  45°  C.     The  bismuth  will 
be  deposited  in  9  hours  in  a  beautiful  form,  free  from 
manganese. 

At  first  the  solution  assumes  a  dark  red  color  due  to 
the  oxidation  of  some  of  the  manganese  into  perman- 
ganic acid.  After  an  hour  or  two  the  color  begins 
gradually  to  fade  away  and  the  solution  again  becomes 
colorless.  A  considerable  quantity  of  hydrated  oxide  of 
manganese  deposits  on  the  anode  during  the  electrol- 
ysis. This  deposit  was  always  examined  for  bismuth, 
but  in  no  case  was  it  found  to  contain  any  of  this  metal 
(Kammerer  and  Am.  Ch.  Jr.,  8,  206). 

15.  From    Molybdenum.      At    present     no    electrolytic 
method  is  known  for  this  purpose. 

16.  From  Mercury.     See  the  separation  of  mercury  from 
bismuth,  p.  146. 

17.  From  Nickel.     The  directions  recorded  on  p.  76  for 
the  determination  of  bismuth  in  acid  solutions  may  be 
followed  with  confidence  in  making  this  separation  (Am. 
Ch.  Jr.,  8,  206;  Jr.  An.  Ch.,  7,  252;  Z.  f.  anorg.  Ch.,  4, 
270). 

18.  From  Palladium  and  Platinum.     Separations  are  not 
known. 


I  62  ELECTRO-CHEMICAL   ANALYSTS. 

19.  From  Potassium.     Follow  the  methods  given  for  the 
determination  of  bismuth  itself,  pp.  75-78. 

20.  From   Selenium.     There   is   no   existing   electrolytic 
method. 

21.  From  Silver.     Freudenberg    (2.  f.  ph.  Ch.,   12,  108) 
uses  the  nitrates  of  the  two  metals,  adds  to  their  solution 
several  cubic  centimetres  of  nitric  acid  of  sp.  gr.   1.2 
and  from  2  to  4  grams  of  ammonium  nitrate,  then  elec- 
trolyzes  with  a  current  having  a  potential  of  1.3  volts. 
The   silver   is   precipitated   through   the   night.     The 
liquid  containing  the  residual  bismuth  may  be  worked 
for  the  determination  of  the  bismuth  by  the  amalgam 
method,  p.  75,  although  it  would  appear  that  Freuden- 
berg always  determined  it  by  evaporation  of  the  nitric 
acid   solution   and   ignition   of   the   residue,    weighing 
finally  bismuth  oxide.     The  results  obtained  by  him 
are: — 

Silver    used,  0.3790  gram  ;   Bi  =  0.3080  gram. 
Silver  found,  0.3793       "       Bi  =  0.3073      " 
Silver    used,  0.2916       "       Bi  =0.3080      " 
Silver  found,  0.2914      "       Bi  =  0.3072      " 

22.  From  Sodium.  Any  one  of  the  methods  pursued  in 
the  determination  of  bismuth  when  alone  will  do  for 
this  purpose  (pp.  75-78). 

23.  From  Strontium.     See  the  separation  of  barium  from 
bismuth,  p.  157. 

24.  From  Tellurium.     There  is  no  recorded  electrolytic 
separation. 

25.  From  Tin.     The  solution  contained  0.0518  gram  of 
bismuth  and  0.1031  gram  of  tin.     To  it  were  added  5 
grams  of  tartaric  acid  and  15  c.c.  of  ammonium  hydrox- 
ide, and  the  liquid  then  diluted  to  175  c.c.  with  water 


SEPARATION  OF  METALS BISMUTH.  163 

and  electrolyzed  at  the  ordinary  temperature  with 
N.D100=  0.02  ampere  and  1.8  volts,  during  the  night 
(J.Am.  Ch.  S.,  15,  204). 

The  chemist  who  proposed  the  preceding  method  also 
separated  bismuth  from  a  mixture  of  arsenic,  antimony, 
and  tin.  The  solution  with  which  he  operated  con- 
tained 0.0518  gram  of  bismuth,  0.1009  gram  of  arsenic, 
0.1024  gram  of  antimony,  and  0.1031  gram  of  tin.  To 
it  were  added  8  grams  of  tartaric  acid  and  3  c.c.  of 
ammonia,  then  diluted  to  175  c.c.  with  water  and  elec- 
trolyzed with  a  current  of  N.D100  ==  0.02  ampere  and 
1.9  volts,  at  the  ordinary  temperature.  The  precip- 
itation was  made  during  the  night.  The  time  factor 
can  probably  be  reduced  by  the  application  of  a  gentle 
heat.  The  bismuth  precipitates  rapidly  and  in  an  ad- 
herent form. 

26.  From  Tungsten.     There  is  no  recorded  separation. 

27.  From  Uranium.     The  conditions  presented  on  p.  76 
for  the  determination  of  bismuth  in  sulphuric  acid  solu- 
tion will  serve  excellently  in  making   this  separation 
(Am.  Ch.  Jr.,  8,  206).    See  also  bismuth  from  chromium. 

28.  From  Vanadium.  There  is  no  recorded  separation. 

29.  From  Zinc.     The  conditions  given  in  the  determina- 
tion of  bismuth  in  nitric  acid  (p.  76),  sulphuric  acid  (p. 
76),  and  as  amalgam  (p.  75)  will  be  found  satisfactory 
in  this  separation  (Am.  Ch.  Jr.,  8,  206;  Jr.  An.  Ch.,  7, 
255).     See  also  bismuth  from  cobalt. 


164  ELECTRO-CHEMICAL    ANALYSIS. 

LEAD. 

The  importance  of  lead  industrially  makes  not  only  its 
accurate  determination  of  interest  and  value,  but  its 
separation  from  the  metals  frequently  associated  with  it 
becomes  a  matter  of  deep  concern.  It  will  be  generally 
conceded  that  lead  is  a  metal  that  is  best  determined  by 
the  electrolytic  procedure;  this  is  vastly  better  than  the 
ordinary  gravimetric  processes,  and  this,  too,  increases  the 
value  of  its  separations. 

1.  From   Aluminium.     As   aluminium   is   not  precipita- 
ted electrolytically  from  a  nitric  acid  solution  and  the 
latter  is  especially  well  adapted  for  the  deposition  of 
lead  in  the  form  of  its  dioxide  upon  the  anode,  the  con- 
ditions laid  down  upon  p.  79  will  be  found  to  answer 
admirably  in  effecting  the  present  separation. 

2.  From  Antimony.     A  purely  electrolytic  procedure  is 
at  the  present  not  known  for  the  separation  of  these 
metals.     In  the  Ch.  Z.,  19,  1142  (1895),  Nissenson  and 
Neumann  described  a  method  for  the  analysis  of  an 
alloy  of  antimony  and  lead,  which  deserves  attention 
here.     It  is  not  an  electrolytic  separation  in  any  sense 
of  that  term,  but  a  helpful  suggestion. 

The  finely  divided  alloy  is  brought  into  solution  with 
4  c.c.  of  nitric  acid  (sp.  gr.  1.4),  15  c.c.  of  water,  and  10 
grams  of  tartaric  acid.  Four  cubic  centimetres  of  con- 
centrated sulphuric  acid  are  added  to  the  clear  solution, 
which  is  then  diluted  with  water,  allowed  to  cool,  and 
rilled  up  to  the  mark  of  the  J-litre  flask.  On  filtering 
from  the  lead  sulphate,  which  has  separated,  the  filtrate 
will  contain  all  of  the  antimony.  None  will  remain  in 
the  lead  sulphate.  Remove  50  c.c.  of  the  filtrate  with  a 


SEPARATION    OF    METALS LEAD.  165 

pipette,  render  it  strongly  alkaline  with  caustic  soda, 
add  50  c.c.  of  a  cold  saturated  sodium  sulphide  solution, 
boil,  filter  at  once,  wash  and  electrolyze  the  hot  solution 
with  a  current  of  N.D100  =  i  .5-2.0  amperes.  An  hour  at 
the  most  will  be  required  for  the  deposition  of  the  anti- 
mony. 

The  lead  sulphate  should  be  digested  for  a  few 
minutes  with  ammonia  water.  This  changes  it  to  hy- 
droxide, which  can  be  gradually  introduced  into  a 
platinum  dish  containing  20  c.c.  of  nitric  acid,  in 
which  it  slowly  dissolves.  The  liquid  is  then  elec- 
trolyzed  with  the  conditions  indicated  on  p.  79. 

3.  From  Arsenic.     Neumann   (Ch.   Z.,  20,  382)   records 
his  experience  in   attempting  to  separate  these  metals 
electrolytically,  from  which  the  conclusion  may  be  de- 
duced that  in  the  presence  of  arsenic  the  lead  determina- 
tions are  not  reliable.     They  are  too  low.     When  there 
is  only  a  fraction  of  a  per  cent,  of  arsenic  present,  the 
results  can  be  used,  although  the  time  then  necessary  for 
the  complete  precipitation  of  the  lead  as  dioxide  is  pro- 
longed to  an  unwarrantable  degree.     The  experiments 
of  Neumann  were  all  conducted  in  nitric  acid  solu- 
tion. 

4.  From    Barium,   Strontium,  Calcium,  Magnesium,   the 
Alkali  Metals,  Beryllium,  Cadmium,  Chromium,  Iron, 
Uranium,    Zirconium,    Zinc,   Nickel,  and    Cobalt    the 
separation  of  lead  is  easily  made  by  observing  the  condi- 
tions   given    (p.    79)    for    its     determination.     There 
should  be  from  15  to  20  per  cent,  of  concentrated  nitric 
acid  present.     The  liquid  poured  off  from  the  deposit 
of  lead  peroxide  is  changed  into  the  most  favorable  salt 
for  the  precipitation  of  the  particular  metal  and  the 
electrolysis  proceeded  with  in  the  usual  way. 


I  66  ELECTRO-CHEMICAL    ANALYSIS. 

5.  From  Bismuth.     Seep.  1 60. 

6.  From  Copper.     This  separation  has  always  been  made 
in  the  presence  of  free  nitric  acid.     The  details  of  pro- 
cedure are  described  under  copper  from  lead,  p.  129. 

7.  From  Gold.     This  combination  of  metals  has  not  re- 
ceived any  attention,  apparently,  in  the  electrolytic 
way  as  the  separation  can  be  made  more  satisfactorily 
in  other  ways. 

8.  From  Manganese  :— 

In  nitric  acid  solution.  It  is  well  known  that  man- 
ganese can  be  precipitated  from  solutions  in  which  the 
quantity  of  free  nitric  acid  does  not  exceed  from  3  to  5 
'per  cent.  Greater  quantities  of  the  acid  prevent  its 
appearance,  its  presence  being  made  evident  by  the 
pink  tinge  of  permanganic  acid  about  the  anode.  As 
lead  is  completely  deposited  even  in  the  presence  of 
from  1 5  to  20  per  cent,  of  acid,  it  would  seem  as  if  the 
separation  could  be  made  under  the  latter  conditions. 
Until  recently  it  has  not  been  undertaken.  Neu- 
mann recommends  heating  the  solution  containing 
the  two  metals  and  20  per  cent,  of  concentrated  nitric 
acid  to  70°,  then  electrolyzing  with  a  current  of  from 
i  .5  to  2  amperes  and  2.5  to  2.7  volts.  It  is  absolutely 
essential  to  use  hot  solutions,  strong  currents,  and 
not  too  large  quantities  of  manganese  (0.03  gram  of 
manganese  at  the  most  in  150  c.c.  of  liquid).  When 
large  amounts  are  employed  and  the  electrolysis  pro- 
longed the  liquid  will  very  probably  become  turbid, 
owing  to  the  separation  of  dioxide  of  manganese  (Ch. 
2.,  20,  383). 

9.  From  Mercury.     The  details  of    this    separation  are 
given  under  mercury  from  lead,  p.  152. 

JO.  From  Selenium.     As  selenium  materially  affects  the 


SEPARATION    OF    METALS LEAD. 


I67 


deposition  of  lead  as  dioxide  from  a  nitric  acid  solution, 
it  may  be  of  interest  to  present  some  results  from  Neu- 
mann's experiments  (Ch.  Z.,  20,  383).  They  are  in- 
structive and  suggestive.  He  used  solutions  of  lead 
nitrate  containing  sodium  selenite.  The  first  experi- 
ment was  with  lead  alone,  the  others  contain  the  two 
metals : — 


LEAD 
PRESENT. 

SELENIUM 
PRESENT. 

NITRIC 
ACID. 

LIQUID. 

TIME. 

AMPERES. 

VOLTS. 

LEAD 
FOUND. 

0.2238 

O.OOO 

30  c.c. 

150  c.c. 

hr. 

0.8 

3 

0.2238 

0.2238 

0.005 

30    « 

150  «« 

« 

0.8 

3 

0.2208 

0.2238 

O.OIOO 

30     " 

150  " 

« 

0.8 

3 

0.2156 

0.2238 

O.O2OO 

30     " 

150  " 

« 

0.8 

3 

0.1886 

0.2238 

0.0500 

30     " 

150  " 

«  « 

0.8 

3 

0.0327 

As    the   quantity   of   selenium    was   increased,    the 
amount  of  lead  dioxide  deposited  grew  less.     This  was 
the  case  with  lead  and  arsenic.     The  cathode  also  car- 
ried a  deposit  consisting  of  metallic  lead  and  selenium. 
11.  From  Silver: — 

In  nitric  acid  solution.  An  example,  taken  from  a  num- 
ber made  in  this  laboratory,  will  give  the  best  condi- 
tions for  carrying  out  this  separation :  To  a  solution 
containing  0.1028  gram  of  silver  and  lead  equal  to 
0.0144  gram  of  dioxide  were  added  15  c.c.  of  nitric  acid 
of  1.3  specific  gravity.  After  dilution  to  200  c.c.  it 
was  electrolyzed  with  a  current  of  N.D100=  0.18  am- 
pere and  2.25  volts.  The  deposit  of  silver  weighed 
0.1023  gram  and  that  of  the  dioxide  0.0144  gram. 
It  is  probably  not  necessary  to  say  that  the  depo- 
sitions were  simultaneous  and  that  the  precautions 
described  under  the  individual  metals  were  carefully 


I  68  ELECTRO-CHEMICAL    ANALYSIS. 

observed.  It  must  be  borne  in  mind  that  silver  quite 
often  separates  in  the  presence  of  nitric  acid  both  as 
peroxide  at  the  anode  and  as  metal  at  the  cathode, 
so  that  Luckow  recommends  the  presence  of  at  least 
1 8  per  cent,  of  nitric  acid  and  also  introduces  several 
drops  of  oxalic  acid,  thus  hindering  the  precipitation 
of  silver  dioxide  (Jr.  An.  Ch.,  7,  252;  Z.  f.  ang.  Ch., 
1890,  345). 

12.  From  Tellurium.     This   separation  has  not  received 
any  attention  as  yet. 

13.  From  Tin.     In  this  instance  the  usual  gravimetric 
procedure  is  the  preferable  course  to  adopt  in  making 
the  separation. 


SILVER. 

The  current  has  proved  a  most  valuable  reagent  in  the 
separation  of  this  metal  from  many  others  which  occur 
associated  with  it.  The  ease  and  accuracy  of  these  vari- 
ous separations  recommend  them. 

1.  From  Aluminium.     The   conditions   given   on   p.   81 
for  the  precipitation  of  silver  from  a  nitric  acid  solu- 
tion will  answer  for  this  separation. 

2.  From  Antimony:— 

(a)  In  ammoniacal  solution.  In  accordance  with  the 
suggestion  of  Fretidenberg  (2.  f.  ph.  Ch.,  12,  109), 
if  the  antimony  be  raised  to  its  highest  state  of  oxida- 
tion it  will  only  be  necessary  to  add  ammonium  sul- 
phate and  ammonia  water  to  the  solution  of  the  com- 
bined metals  and  electrolyze  with  a  current  having  a 
pressure  varying  from  1.2  to  1.3  volts.  Theprecip- 


SEPARATION    OF    METALS SILVER.  169 

itated  metal  will  not  adhere  well  to  the  dish,  so  that 
the  method  will  be  used  only  when  special  reasons 
demand  it. 

(b)  In  acid  solution.     To  the  nitric  acid  solution  add 
tartaric  acid,   after  having  converted  all  the  anti- 
mony into  pentoxide,  and  electrolyze  with  a  pressure 
not  exceeding  1.4  to  1.5  volts.    Freudenberg  remarks 
that  the  deposit  of  silver  is  not  well  suited  for  weigh- 
ing. 

(c)  In    potassium    cyanide    solution.     The    antimony 
should    exist    as    pentoxide.     After    adding  tartaric 
acid  to  the  cyanide  solution  (i  gram  of  pure  potas- 
sium cyanide  for  every  o.i  gram  of  metal),  electrolyze 
with  a  pressure  of  from  2.3  to  2.4  volts. 

3.  From  Arsenic.     The  methods  just  described  for  the 
separation  of  silver  from  antimony  will  be  found  appli- 
cable in  this  case  (Am.  Ch.  Jr.,  12,  428). 

4.  From  Barium.     Follow  the  instructions  given  on  p.  8 1 
for  the  determination  of  silver. 

5.  From  Bismuth.     See  p.  162,  bismuth  from  silver. 

6.  From  Cadmium:— 

(a)  In  nitric  acid  solution.     To  the  solution  of  the  salts 
of  the  two  metals  add  15  to  20  c.c.  of  nitric  acid  of 
specific  gravity     1.3,   heat   to   60°,   and   electrolyze 
with  a  current  having  a   pressure  of  from  2  to  2.2 
volts.     The  silver  will  be  precipitated  and  should  be 
treated  as  directed  on  p.  81.     The  acid  filtrate  can, 
by  the  addition  of  an  excess  of   sodium  acetate,  be 
changed  to  a  suitable  form  for  the  deposition  of  the 
cadmium.     See  p.  69. 

(b)  In  potassium  cyanide  solution.     Add   2   grams  of 
pure  potassium  cyanide  to  the  solution,  containing 
0.1-0.2  gram  of  each  metal,  dilute  to  125  c.c.,  heat  to 

15 


I  70  ELECTRO-CHEMICAL    ANALYSIS. 

65°-75°,  then  conduct  a  current  of  N.D100  ==  0.02- 
0.025  ampere  and  2.1  volts  through  the  liquid. 
The  silver  will  be  completely  precipitated  at  the 
expiration  of  from  4  to  5  hours.  After  removing 
the  liquid  from  the  precipitating  dish  it  should  be 
reduced  in  volume,  introduced  into  a  second  weighed 
platinum  dish,  and  electrolyzed  as  described  on  p. 
68  for  the  deposition  of  the  cadmium. 

7.  From  Calcium  and  Chromium.     See  p.  168. 

8.  From  Cobalt.     An  example  will  show  the  conditions 
which  have  been  found  very  satisfactory  in  this  particu- 
lar separation :  To  the  solution  of  the  silver  salt  (0.1024 
gram  of  silver)  were  added  o.  i  gram  of  cobalt  as  nitrate 
and  2.75  grams  of  pure  potassium  cyanide.     The  liquid 
was  diluted  to  125  c.c.  with  water,  heated  to  65°  C.,  and 
electrolyzed  with  N.D100  =  0.038  ampere  and  2  volts. 
At  the  expiration  of  5  hours  the  silver  was  completely 
deposited.     It  weighed  0.1027  gram.     It  contained  no 
cobalt  (J.  Am.  Ch.  $.,  21,  915).     This  procedure  is  pref- 
erable to  the  deposition  of    silver  from  a  nitric  acid 
solution. 

9.  From  Copper  :— 

(a)  In  nitric  acid  solution.  Freudenberg  added  2  to  3 
c.c.  of  nitric  acid  of  1.2  specific  gravity  to  the  solution 
of  salts  of  the  two  metals,  then  electrolyzed  with  a 
pressure  of  1.3-1.4  volts,  and  a  current  of  o.  i  ampere. 
The  silver  was  deposited  free  from  copper  (Z.  f.  ph. 
Ch.,  12,  107;  Berg-Hutt.  2.  (1883),  375). 

At  the  ordinary  temperature  this  separation  will 
require  7  hours,  while  at  60°  the  precipitation  of  the 
silver  will  be  finished  in  4  hours.  The  liquid  siphoned 
off  from  the  silver,  after  the  addition  of  nitric  acid, 
can  be  electrolyzed  in  a  beaker  glass  in  which  a  plati- 


SEPARATION    OF    METALS SILVER.  I  7! 

num  cone  is  suspended.  The  copper  is  precipitated 
on  the  cone.  A  current  ranging  from  0.5  to  i.o  am- 
pere will  be  required  for  this.  The  solution  should 
be  heated  to  6o°-65°. 

The  plan  is  ideal,  but  those  who  have  attempted  to 
repeat  Freudenberg's  work  have  encountered  diffi- 
culties, and  naturally  modifications  of  the  procedure 
have  been  proposed.  Kiister  and  v.  Steinwehr  (Z.  f. 
Elektrochem.,  4,  451),  in  particular,  have  made  an 
exhaustive  investigation  of  the  precipitation  of  silver 
from  nitric  acid  and  its  separation  from  copper  in  the 
presence  of  the  latter  acid.  Their  conclusion  is 
briefly  that  the  solution  should  contain  from  i  to  2 
c.c.  of  nitric  acid  (sp.  gr.  1.4),  and  that  to  it  should 
be  added  5  c.c.  of  alcohol.  Further,  that  the  poten- 
tial of  the  electrolyte  should  be  kept  constantly  at 
I-35~I-38  volts.  An  example  will  show  how  they 
operated:  A  weighed  piece  (0.3161  gram)  of  silver 
coin  was  dissolved  in  2  c.c.  of  nitric  acid  (sp.  gr.  1.4), 
the  liquid  was  diluted  to  150  c.c.,  5  c.c.  of  alcohol 
were  added,  and  the  solution  then  heated  to  55°  and 
electrolyzed  with  i.36jf  o.oi  volt.  They  obtained 
0.2839  gram  of  silver  =  89.83  per  cent. 
(b)  In  potassium  cyanide  solution.  This  separation  was 
first  made  by  Smith  and  Frankel  (Am.  Ch.  Jr.,  12, 
104)  and  has  been  carried  out  over  a  hundred  times  in 
this  laboratory  by  experienced  persons  and  by  those 
who  lacked  experience,  but  in  all  cases  the  results 
have  been  most  satisfactory. 

Add  2  grams  of  pure  potassium  cyanide  to  the  solu- 
tion of  mixed  salts,  heat  to  65°,  and  electrolyze  the 
liquid  (125  c.c.)  with  a  current  of  N.D100  =  0.03-0.058 
ampere  and  1.1-1.6  volts.  The  silver  will  be  precipi- 


172  ELECTRO-CHEMICAL   ANALYSIS. 

tated  in  from  4  to  5  hours.  It  will,  of  course,  be 
understood  that  if  there  be  a  great  preponderance  of 
copper  over  the  silver  the  quantity  of  potassium  cy- 
anide will  have  to  be  increased.  Example:  A  solu- 
tion contained  0.1066  gram  of  silver  and  0.5265  gram 
of  copper.  Four  grams  of  pure  potassium  cyanide 
were  added,  the  liquid  was  heated  to  60°  and  elec- 
trolyzed  for  3^  hours  with  a  current  of  N.D]00  =  0.02- 
0.03  ampere  and  1.2  volts.  The  silver  deposit 
weighed  0.1066  gram.  The  total  dilution  was  125 
c.c. 

The  presence  of  three  or  four  metals  besides  the 
silver  also  requires  the  addition  of  more  alkaline 
cyanide  (J.  Am.  Ch.  S.,  23,  582,  also  Brunck,  Ber., 
34,  1604;  Revay,  Z.  f.  Elektrochem.,  4,  313). 

10.  From    Gold.     No    successful    method   has   yet   been 
found.     See  Jr.  An.  Ch.,  6,  87. 

11.  From  Iron.     When  the  iron  is  present  as  a  ferrous 
salt  in  the  mixture  of  salts,  introduce  into  the  solution 
3  grams  of  potassium  cyanide,  dilute  to  100  c.c.  with 
water,  heat  to  65°,  and  electrolyze  with  a  current  of 
N.D100=  0.04  ampere  and  2.7  volts.     The  silver  will  be 
fully  precipitated  in  3  hours. 

The  separation  of  these  metals  can  also  be  made  in 
nitric  acid  solution  by  observing  the  conditions  laid 
down  on  p.  81. 

12.  From  Lead.     Consult  p.  167,  where  the  separation  of 
lead  from  silver  is  described. 

13.  From  Lithium.     See  silver  from  barium  and  the  alka- 
line earth  metals,  p.  169. 

14.  From  Magnesium.     See  silver  from  barium,  p.  169. 

15.  From  Manganese.     See  lead  from  manganese,  p.  166. 

1 6.  From    Mercury.     There    is    no    known    electrolytic 


SEPARATION    OF    METALS SILVER.  173 

method  for  the  separation  of  these  metals.  It  is  true 
that  both  can  be  precipitated' from  a  nitric  acid  solution 
(pp.  72,  81),  their  joint  weight  be  determined,  after 
which  the  mercury  can  be  expelled  by  heat  and  the 
silver  residue  be  reweighed. 

17.  From  Molybdenum,  Tungsten,  and  Osmium.     Follow 
the  conditions  recommended  as  satisfactory  in  the  sep- 
aration of  silver  from  cobalt,  p.  170. 

18.  From  Nickel.     Add  1.5  grams  of  pure  potassium  cy- 
anide to  the  solution  containing  equal  amounts  of  the 
metals  (0.1-0.2  gram),  dilute  to   125  c.c.  with  water, 
heat  to  6o°-65°,  and  electrolyze  with  a  current  of  N.D100 

0.02-0.03  ampere  and  a  pressure  of  1.6-2.0  volts. 
The  period  of  precipitation  is  usually  three  hours  (J. 
Am.  Ch.  S.,  21,  915). 

19.  From    Palladium.      The    electrolytic    separation    of 
silver  from  palladium  has  not  yet  been  made  with  any 
satisfaction. 

20.  From   Platinum.     To  the  solution  of  the  combined 
metals  add  (for  0.2  gram  of  each  metal)  1.25  grams  of 
pure  potassium  cyanide,  dilute  to  125  c.c.  with  water, 
heat  to  70°,  and  electrolyze  with  a  current  of  N.D100  = 
0.04  ampere  and  2.5  volts.     The  precipitation  will  be 
complete  at  the  end  of  3  hours  (J.  Am.  Ch.  S.,  21,  913). 

21.  From  Potassium,  the  other  Alkali  Metals,  and  Alka= 
line  Earth  Metals.     See  the  separation  from  barium, 
p.  169. 

22.  From   Selenium   and   Tellurium.     These   separations 
have  not  yet  been  made  in  the  electrolytic  way. 

Since  this  paragraph  was  written  Meyer  (Z.  f. 
anorg.  Ch.,  31,  393)  pursued  a  course  in  the  deter- 
mination of  the  atomic  weight  of  selenium,  in 
which  he  electrolyzed  silver  selenite  in  cyanide  so- 


174  ELECTRO-CHEMICAL    ANALYSIS. 

lution.  The  silver  was  precipitated  free  from 
selenium,  so  that  this -method  may  be  regarded  as 
furnishing  a  satisfactory  separation  of  the  two 
metals.  Perhaps  tellurium  can  be  similarly  separ- 
ated from  silver. 

23.  From  Tin.     When  tin  and  silver  are  present  together, 
digest  their  sulphides  with  ammonium  sulphide,  which 
will  bring  the  tin  into  a  proper  condition  to  effect  its 
determination  electrolytically   (p.    113).     Dissolve  the 
insoluble  silver  sulphide  in  nitric  acid,  and  after  the 
excess  of  the  latter  is  expelled,  add  an  excess  of  potas- 
sium cyanide  and  proceed  as  directed  on  p.  83.     The 
silver  will  be  deposited  as  a  dense  coating,  and  may 
be  washed  with  hot  water. 

This  same  course,  which  is  not  a  strict  electrolytic  pro- 
cedure, has  also  been  recommended  for  the  separation  of 
silver  when  associated  with  arsenic,  antimony,  and  tin. 

24.  From  Uranium.     See  aluminium  from  silver,  p.  1 68. 

25.  From  Zinc.     Add  i  gram  of  pure  potassium  cyanide 
to  the  liquid  containing  at  least  o.i  gram  of  each  metal, 
dilute  to  125  c.c.  with  water,  and  electrolyze  at   70° 
with  a  current  of  N.D100  =  0.032-0.038  ampere  and  2.76 
volts.     The  silver  will  be  fully  precipitated  in  3  hours. 
Treat  as  described  on  p.  83  (J.  Am.  Ch.  S.,  21,  915). 


GOLD. 

Separations  of  gold  from  certain  metals  have  been  car- 
ried out  in  the  electrolytic  way  with  marked  success. 
As  they  may  prove  helpful,  it  was  deemed  advisable  to 
describe  them  here  in  sufficient  detail  to  make  them  gener- 
ally applicable. 


SEPARATION    OF    METALS GOLD.  175 

1.  From  Antimony.     Add  0.5  to  i  gram  of  tartaric  acid 
to  their  solution,  followed  by  3   to   4  grams '  of  pure 
potassium  cyanide ;  then  electrolyze  with  the  conditions 
given  under  the  separation  of  gold  from  copper. 

2.  From  Copper.     The  alkaline  cyanide  solution  is  best 
adapted  for  this  separation.     To  the   liquid   contain- 
ing 0.1665  gram  of  gold  and  a  like  amount  of  copper 
4  grams  of  potassium  cyanide  were  added.    The  solution 
was  diluted  to  250  c.c.  with  water,  heated  to  6o°-65°, 
and  electrolyzed  with  a  current  of  N.D100=  0.05-0.08 
ampere  and  1.7-1.9  volts.     At  the  expiration  of  two 
and  one-half  hours  0.1667   gram  of   gold,   free  from 
copper,  was  precipitated.     The  liquid  poured  off  from 
the  gold,  after  the  addition  of  an  excess  of  ammonium 
carbonate,  can  be  acted  upon  with  a  more  powerful 
current    and    the    copper   be   thus   obtained   (p.  65). 
See  J.  Am.  Ch.  S.,  21,  921. 

3.  From   Cobalt.      In   the    early    experiments    made    in 
the  separation    of  these  metals  some  difficulties  were 
encountered,  so  that    it  will   be    necessary    to    follow 
the  directions,   given    below,  with    the    utmost   care. 
After  adding  4  grams  of  pure  potassium  cyanide  to  the 
solution,  dilute  to  125  c.c.,  heat  to  65°,  and  electrolyze 
with  a  current  of  N.D100=  0.05-0.08  ampere  and  1.7-2 
volts.     Before  interrupting  the  current  introduce  i  c.c. 
of  a  2  per  cent,  sodium  hydroxide  solution  and  increase 
the  current  to  o.io  ampere.     The  time  necessary  to 
effect  this  separation  is   usually  6   hours  (J.  Am.  Ch. 
S.,  21,  922). 

4.  From  Nickel.     Follow  the  conditions  observed  in  the 
separation  of  gold  from  cobalt  (see  above). 

5.  From  Palladium.    To  their  solution   add    2   grams  of 
pure  potassium  cyanide,  dilute  to  150  c.c.  with  water, 


176  ELECTRO-CHEMICAL    ANALYSIS. 

heat  to  65°,  and  electrolyze  for  5  hours  with  a  current 
of  N.D100  ==  0.03  to  0.06  ampere  and  2.5  volts.  The 
gold  will  be  precipitated  free  from  palladium. 

6.  From    Platinum.     Add    to    the    solution,    containing 
equal  quantities  of  the  two  metals,  about  1.5  grams  of 
pure  potassium  cyanide,  dilute  to  250  c.c.  with  water, 
heat  to  70°,  and  electrolyze  for  3  hours  with  a  current  of 
N.D100=  o.oi  ampere  and  2.7  volts  (J.  Am.  Ch.  $.,  21, 

923)- 

7.  From  Zinc.     In  this  separation  the  points  to  be  ob- 
served are  the  quantity  of  potassium  cyanide  (4  grams), 
the  current    density,   N.D100  ==   0.06    ampere,  and  the 
pressure,  which  should  be  about  2.6  volts.     The  dilu- 
tion and  other  conditions  are  similar  to  those  followed 
in  the  separation  of  gold  from  copper,  p.  175  (J.   Am. 
Ch.  S.,  21,923). 

It  may  be  here  stated  that  the  conditions  given  for 
the  separation  of  gold  from  copper  will  serve  equally  well 
for  the  separation  of  gold  from  molybdenum,  tungsten, 
and  osmium.  The  conditions  observed  in  the  precipi- 
tation of  gold  from  a  sulphaurate  solution  (p.  1 1 1)  can 
be  used  with  the  certainty  of  good  results  in  the  sepa- 
ration of  gold  from  arsenic,  molybdenum,  and  tungsten, 
while  its  deposition  from  a  phosphoric  acid  solution  (p. 
in)  will  prove  of  value  in  its  separation  from  zinc 
and  cobalt  (Am.  Ch.  Jr.,  13,  206). 


THE   PLATINUM   METALS. 

The  separations  in  this  group  of  metals  are  not  nu- 
merous. Platinum  itself  may  be  separated  in  an  acid 
solution  from  zinc,  cadmium,  iron,  nickel,  and  cobalt  by 


SEPARATION    OF    METALS ANTIMONY.  177 

using  a  current  of  N.D100=  0.07-0.08  ampere  and  1.8-2.0 
volts.  Palladium  can  be  separated  from  iridium  by 
means  of  the  method  given  on  p.  106  for  its  determination. 
Platinum  can  be  separated  from  iridium  in  a  similar  man- 
ner, with  a  current  of  N.Dloo=  0.05  ampere  and  1.2  volts 
(Classen).  Although  rhodium  can  be  completely  precip- 
itated from  an  acid  phosphate  solution  (p.  107),  it  can- 
not be  thus  separated  from  iridium. 


ANTIMONY,   ARSENIC,   AND   TIN. 

Under  the  metals  which  precede  this  group  will  be  found 
the  methods  that  experience  has  shown  are  best  adapted 
for  their  separation  from  any  one  member  of  this  group. 
So  far  as  the  latter  itself  is  concerned,  much  credit  is  due 
Classen  and  his  co-laborers  for  valuable  data  upon  the 
electrolytic  separation  of  its  members. 

1.  Antimony  from  Arsenic.     The  metals,  or  compounds 
of  the  same,  are  evaporated  to  dry  ness  with  aqua  regia, 
the  residue  dissolved  in  2  to  3  c.c.  of  water;  concen- 
trated sodium  hydroxide  is  added  so  that  there  will  be 
2.5  grams  of  alkali  present  in  the  liquid  and  then  80  c.c. 
of  sodium  sulphide  (sp.gr.  1.13-1.15)  are  introduced  and 
the  whole  solution  is  diluted  to  150  c.c.,  temperature 
25°-38°,  and    electrolyzed   with    N.D100=    1.5-1.6  am- 
peres and  2.1  volts  (beginning)  to  1.45  volts  (at  end). 
The  time  required  for  the  separation  of  the  antimony 
is  usually  6  hours  (Z.  f.  Elektrochem.,  1,  291). 

2.  Antimony  from  Tin.     The  sulphides  (or  residue  from 
a  solution  of  the  metals)  are  placed  in  a  weighed  plati- 
num dish  and  covered  with  80  c.c.  of  sodium  sulphide 

16 


178  ELECTRO-CHEMICAL    ANALYSIS. 

of  specific  gravity  1.13-1.15,  to  which  are  added  2 
grams  of  sodium  hydroxide.  Dilute  to  125  c.c.  with 
water,  heat  to  57°-67°,  and  electrolyze  with  a  current 
of  N.Dloo  ==  1.45-1.50  amperes  and  0.9-0.8  volt.  The 
precipitation  will  be  complete  at  the  expiration  of  2 
hours  (Z.  f.  Elektrochem.,  1,  291).  Pour  off  the  liquid 
into  a  second  dish.  Treat  the  deposit  of  antimony  as 
previously  directed  (p.  115).  To  prepare  the  tin  solu- 
tion for  electrolysis,  proceed  as  described  (p.  113)  for 
the  conversion  of  the  sodium  into  ammonium  sulphide 
(Ber.,  17,2245;  18,  mo). 

This  separation  has  not  always,  in  the  hands  of  chem- 
ists, given  the  results  that  were  confidently  expected. 
There  are  disturbing  features  connected  with  it.  It  is 
not  certain  that  these  have  been  absolutely  eliminated, 
although  strenuous  efforts  have  been  put  forth  to  arrive 
at  such  a  result.  Very  recently  Ost  and  Klapproth 
(Z.  f.  ang.  Ch.,  1900,  p.  827)  conducted  experiments  in  a 
cell  provided  with  a  diaphragm  (p.  117).  These  dem- 
onstrated that  by  using  a  concentrated  sodium  sul- 
phide solution  the  current,  as  a  rule,  mainly  decom- 
poses the  sodium  sulphide,  and  the  antimony,  if  the 
bath  pressure  is  low,  does  not  participate  in  the  electrol- 
ysis. It  is  precipitated  as  a  secondary  product  by  the 
sodium  ion.  When  the  pressure  is  great  and  the  anti- 
mony salt  assists  in  conducting  the  current,  then  the 
antimony  wanders  in  the  form  of  a  complex  anion, 
SbS4,  to  the  anode.  Disturbances  also  arise  from  the 
commingling  of  the  anode  and  cathode  liquids,  so  that 
these  investigators  have  worked  out  the  follow- 
ing piece  of  apparatus,  to  be  used  in  this  separation, 
which  in  their  hands  has  yielded  very  satisfactory 
results.  The  sketch  (Fig.  38)  gives  a  perfect  idea 


SEPARATION    OF    METALS ANTIMONY. 


179 


of  their  scheme,  a  is  a  low  beaker  glass;  the  cylin- 
drical diaphragm  (a  Pukall  porous  cell),  b,  stands  in  it. 
The  anode  is  a  rod  of  carbon,  c,  placed  within  the 
diaphragm-cell,  while  a  bent  sheet  of  platinum  or  a 

FIG.  38. 


platinum  gauze,  d,  serves  as  cathode.  The  beaker 
and  cell  are  covered  with  suitable  cover-glasses.  The 
diaphragm-cell  above  the  liquid  is  covered  with  a 
suitable  rubber  ring,  e,  so  that  the  drops  of  liquid  fall- 
ing from  the  cover-glass  are  returned  to  the  cathode 


i8o 


ELECTRO-CHEMICAL    ANALYSIS. 


chamber.  The  diaphragm,  thoroughly  cleaned,  should 
always  be  preserved  under  water.  The  anode  liquor 
should  be  introduced  into  the  diaphragm-cell  some 
time  before  the  electrolysis  begins  and  the  appa- 
ratus should  not  be  connected  up  until  this  liquor 
has  penetrated  through  the  walls  of  the  diaphragm. 
During  the  electrolysis  the  level  of  the  anode  solution 
should  stand  from  0.5  to  i  cm.  higher  than  that  of  the 
cathode  solution.  The  anode  chamber  contains  from 
40  to  50  c.c.,  and  the  cathode  chamber  i5oc.c.  The 
total  volume  of  the  electrolytes  is  about  150  c.c.  The 
available  surface  of  the  cathodes  equals  i  sqd  m. 

To  illustrate  the  practical  working  of  this  idea,  sev- 
eral results  taken  from  Klapproth's  doctoral  thesis 
(Die  Fallung  des  Zinns  und  seine  Trennung  vom  Anti- 
mon  durch  Elektrolyse,  Hannover,  1901)  may  here 
be  incorporated: — 


SEPARATION  OF  ANTIMONY  AND  TIN. 

BON  ANODE. 


DIAPHRAGM  AND  CAR- 


X 

00 

5 

,£ 

SOLUTION  OF  90  C.c.  IN 

id 

id 

J 

o 

p~ 

II 

CATHODE  CHAMBER. 

SOLUTION 

p 

S  w 

•^ 

O  ui 

o 
o5 

OF 

^ 

—   !4 

g 

ti,  g 

50  C.c.  IN 

et 

t/5  °* 

fc 

>•  < 

z  z 

ANODE 

a 

H< 

s 

oO 

o  o 

CHAMBER. 

«g 

a 

D 

h  H 

Na2S, 

Sb, 

Sn, 

u 

05  2 

C/! 
f3 

P 

«  H 

IN 

IN 

IN 

* 

£3 

* 

D  Q^ 

C.C. 

GRAMS. 

GRAMS. 

U 

PH 

"^ 

QU 

40 

0.1500 

0.2500 

30  Na2S 

20° 

0.08 

0.9     0.1505 

16 

35 

0.1500 

0.2500 

30  N;i2S 

20° 

0.19 

1.  10 

o.  1446 

7 

60 

0.1500 

0.5000 

f  20(NH4),S      | 
\30(NH4)2S04/ 

20° 

0.2 

0-5 

0.1500 

16 

40 

0.3000 

0.2500 

(  2o(NH4^2S      i 

20° 

0.15 

1.2 

0.2990 

7 

5o 

0.150 

0.2500 

i  2o(NH4)2S    ^  ) 
\3o(NH4)2S04f 

20° 

0-5 

I.O 

0.1495 

16 

SEPARATION    OF    METALS ARSENIC,  TIN.  l8l 

The  solution,  freed  from  antimony,  can  now  be 
changed  to  one  suitable  for  the  precipitation  of  the  tin 
by  digesting  it  with  ammonium  sulphate  (p.  113).  If 
this  is  to  be  done  in  the  absence  of  the  diaphragm,  then 
the  latter  must  be  removed  from  the  solution,  placed 
over  the  cathode  beaker  glass,  and  be  washed  for 
one-half  hour,  by  allowing  water  to  run  through  it. 
The  liquid  is  later  concentrated  and  electrolyzed  (see 
p.  114). 

But  the  tin  may  be  estimated  without  removing  the 
diaphragm.  To  this  end  the  cathode  liquor  is  reduced 
to  a  volume  of  40  c.c.  and  the  anode  solution  is  renewed. 
The  precipitation  of  the  tin  is  then  made  at  70°.  As 
much  as  0.25  gram  of  the  metal  will  be  precipitated  in 
from  2  to  3  hours.  The  pressure  should  not  exceed  2 
volts. 

When  antimony,  arsenic,  and  tin  are  present  together, 
expel  the  arsenic  from  their  solution  by  the  Fischer- 
Huf schmidt  method  (Ber.,  18,  mo),  and  separate  the 
antimony  from  the  tin  as  already  described  on  page 
177. 

In  general  analysis  phosphoric  acid  is  frequently  pre- 
cipitated as  tin  phosphate.  The  latter,  of  course,  con- 
tains tin  oxide.  Dissolve  the  precipitate  in  ammonium 
sulphide.  On  electrolyzing  the  solution  the  tin  will  be 
precipitated,  and  the  filtrate  will  contain  all  of  the  phos- 
phoric acid;  this  can  be  estimated  in  the  usual  way 
(Classen).  By  observing  this  suggestion  the  deter- 
mination of  the  phosphoric  acid  in  a  separate  portion  of 
the  material  will  not  be  required. 


I  82  ELECTRO-CHEMICAL    ANALYSIS. 


IRON,    MANGANESE,    NICKEL,    ZINC,    COBALT, 
ALUMINIUM,   CHROMIUM,   AND   PHOS- 
PHORIC ACID. 

Electrolytic  methods  for  the  separation  of  these  metals 
are  neither  so  numerous  nor  so  thoroughly  worked  out  as 
with  the  metals  already  considered.  Their  separation 
from  the  heavy  metals  has  been  outlined  under  the  same, 
and  it  only  remains  to  describe  the  courses  which  may 
be  pursued  with  this  group  of  metals  when  present 
together. 

1.  Iron  from  Aluminium.  Add  sufficient  ammonium 
oxalate  to  the  solution  of  the  salts  of  the  metals  (prefer- 
ably not  chlorides)  so  that  it  will  contain  from  2  to  3 
grams  of  oxalate  for  each  o.  i  gram  of  metal.  Dilute  to 
175  c.c.,  heat  to  40°,  and  electrolyze  with  N.D100  = 
1.95-1.6  amperes  and  4.3-4.4  volts.  The  iron  will  be 
precipitated  in  two  and  one-half  hours  (Ber.,  18,  1795; 
27,  2060;  Z.  f.  Elektrochem.,  1,  292).  It  is  not  ad- 
visable to  allow  the  current  to  act  longer  than  is  neces- 
sary for  the  reduction  of  the  iron.  Towards  the  end  of 
the  electrolysis  aluminium  hydroxide  is  apt  to  separate 
and  will  coat  the  iron  deposit.  When  the  latter  is  dry, 
this  adhering  material  can  be  removed  with  a  handker- 
chief. The  aluminium  must  be  determined  gravi- 
metrically.  The  separation  of  aluminium  hydroxide 
can  be  avoided  if  ammonium  or  potassium  tartrate 
(i  gram)  or  citrate  be  added  to  the  solution  of  the  two 
metals,  and  it  be  heated  to  60°,  then  electrolyzed  with 
N.D100  =  i  ampere  and  4-5  volts.  It  is  true  that  the 
iron  will  probably  contain  small  amounts  of  carbon. 


SEPARATION    OF    METALS IRON.  183 

These  will  not  be  excessive  and  will  not  affect  the  results 
seriously.  See  p.  100. 

Drown  and  McKenna  have  endeavored  to  utilize  the 
method  described  on  p.  101  for  the  separation  of  iron 
from  other  elements.  The  conditions  favorable  for  the 
deposition  of  the  iron  they  found  unfavorable  for  its 
separation  from  manganese.  They  experienced  no 
difficulty  in  separating  iron  from  aluminium  or  iron 
from  phosphoric  acid.  It  is  expected  that  the  process 
will  give  equally  good  results  in  the  separation  of  iron 
and  some  other  metals  from  titanium,  zirconium,  co- 
lumbium,  and  tantalum  (WolcottGibbs,  Am.  Ch.  Jr.,  13, 
571) .  To  determine  iron  in  the  presence  of  aluminium  in 
steel  they  recommend  the  following  procedure : — 

"  Dissolve  5-10  grams  of  iron  or  steel  in  sulphuric 
acid,  evaporate  until  white  fumes  of  sulphuric  anhy- 
dride begin  to  come  off,  add  water,  heat  until  all  the 
iron  is  in  solution,  filter  off  the  silica  and  carbon,  and 
wash  with  water  acidulated  with  sulphuric  acid.  Make 
the  filtrate  nearly  neutral  with  ammonia,  and  add 
to  the  beaker  in  which  the  electrolysis  is  made  about 
100  times  as  much  mercury  as  the  weight  of  iron  or 
steel  taken.  The  volume  of  the  solution  should  be  from 
300  to  500  c.c.  Connect  with  battery  or  dynamo  in 
such  a  way  that  about  2  amperes  may  pass  through  the 
solution  overnight.  .  .  t  When  the  solution  gives 
no  test  for  iron,  it  is  removed  from  the  beaker  with  a 
pipette  while  the  current  is  still  passing."  The  alumi- 
nium is  determined  in  this  filtrate  (Jr.  An.  Ch.,  5,  627). 
2.  From  Chromium.  They  can  be  separated  in  oxalate 
solution  with  conditions  like  those  given  above  for 
the  separation  of  iron  from  aluminium,  the  only  differ- 
ence being  that  the  temperature  should  be  about  65° 


184  ELECTRO-CHEMICAL    ANALYSIS. 

(2.  f.  Elektrochem.,  1,  292).  The  chromium  during  the 
electrolysis  is  converted  into  chromate.  It  must  be  de- 
termined gravimetrically.  The  second  course,  tartrate 
or  citrate  solution,  also  lends  itself  well  to  this  separa- 
tion. The  requisites  are  given  above  under  iron  and 
aluminium.  It  may  be  added  here  that  just  as  iron  is 
separated  in  tartrate  or  citrate  solution  from  aluminium 
and  chromium,  so  can  it  also  be  separated  from  titanium. 

3.  From  Cobalt.     Classen  (Ber.,  27,  2060)  adds  about  8 
grams   of   ammonium   oxalate   to   the  solution  of  the 
metals,  dilutes  with  water  to  120  c.c.,  heats  to  65°-7o°, 
and  electrolyzes  with   N.D100   =      1.6-2.0  amperes  and 
electrode    pressure    of    3.0-3.6    volts.     The    time   re- 
quired for  complete  deposition  varies  from  2  to  4  hours. 
The  metals  are  precipitated  together,  their  combined 
weight  ascertained,  then  they  are  dissolved  in  acid,  and 
the  quantity  of  iron  is  found  by  titration.     The  cobalt 
is  obtained  by  difference. 

Vortmann  suggests  adding  3  to  6  grams  of  ammo- 
nium sulphate  and  a  moderate  excess  of  ammonium 
hydroxide  to  the  solution  of  the  metals,  then  electro- 
lyzing  with  a  current  of  N.D100  ==  0.4-0.8  ampere  and 
4-5  volts.  He  remarks  that  by  contact  with  the  ferric 
hydroxide  the  deposit  of  cobalt  will  contain  traces  of 
iron,  which  can  be  fully  eliminated  by  a  second  precipi- 
tation. (See  iron  from  nickel.) 

4.  From  Manganese.     In  considering  this  separation  it 
should  be  remembered   that  objections   have  repeat- 
edly been  offered  to  the  suggestion  of  Classen  (Ber., 
18,  1787) ;  hence  to  obtain  results  at  all  satisfactory  it  is 
advisable  to  carry  out  the  separation  exactly  as  given  by 
this  chemist:  "  If  a  solution  of  the  double  oxalates  of 
iron  and  manganese  is  subjected  to  electrolysis,  without 


SEPARATION    OF    METALS IRON.  185 

the  previous  addition  of  a  great  excess  of  ammonium 
oxalate  .  .  .  it  is  impossible  to  obtain  a  quantita- 
tive separation  of  the  two  metals,  because  the  man- 
ganese dioxide  carries  down  with  it  considerable  quan- 
tities of  ferric  hydroxide.  The  complete  separation  of 
the  metals  is  possible  only  when  the  separation  of  the  di- 
oxide is  delayed  till  most  of  the  iron  is  precipitated." 
The  electrolysis  in  the  cold  is  not  favorable;  the  large 
amount  of  ammonium  carbonate,  or  ammonia  formed 
in  the  decomposition  of  the  excessive  ammonium  oxal- 
ate, dissolves  the  precipitated  dioxide.  "The  rapid 
dissociation  of  ammonium  oxalate  when  heated,  how- 
ever, gives  a  simple  means  of  delaying,  or  entirely  pre- 
venting, the  formation  of  a  manganese  precipitate 
during  the  electrolysis."  The  solution  containing  the 
two  metals  is  treated  with  8  to  10  grams  of  ammonium 
oxalate  and  while  hot  (70°)  is  acted  upon  with  a  current 
of  N.Dloo  ==  0.5  ampere  and  3.1-3.8  volts.  Treat  the 
iron  deposit  as  directed  on  p.  99.  Boil  the  liquid, 
poured  off  from  the  iron,  with  sodium  hydroxide,  to  de- 
compose the  ammonium  carbonate  present,  after  which 
add  sodium  carbonate  and  a  little  sodium  hypochlorite. 
The  manganese  is  precipitated  as  dioxide,  and  after  solu- 
tion in  hydrochloric  acid  is  finally  weighed  as  pyro- 
phosphate. 

Classen  mentions  that  the  method  affords  good  re- 
sults if  the  manganese  content  is  not  too  high.  In  the 
analysis  of  ferromanganese,  for  example,  it  possesses 
no  practical  value  (Ber.,  18,  1787).  Engels  has  tried 
to  use  the  plan  he  describes  for  the  deposition  of  man- 
ganese (p.  97)  in  effecting  the  separation  of  the  latter 
from  iron  (2.  f.  Elektrochem.,  2,  414),  but  it  has  been 
observed  that  while  the  manganese  was  completely  de- 


I  86  ELECTRO-CHEMICAL    ANALYSIS, 

~    ~s 

posited  as  dioxide,  it  invariably  contained  as  much  as 
0.02  gram  of  iron. 

5.  From  Nickel.  Classen  deposits  nickel  and  iron  together 
(same  as  cobalt  and  iron)  as  an  alloy,  which  is  weighed, 
then  dissolved  in  concentrated  hydrochloric  acid,  the 
iron  oxidized  with  hydrogen  peroxide,  and  the  ferric  so- 
lution titrated  with  a  stannous  chloride  solution.  The 
current  may  vary  from  1.75  to  2.2  amperes  and  the  volt- 
age from  3.4  to  4.0.  The  temperature  of  the  liquid  is 
usually  65°-7o°.  Two  hours  will  be  sufficient  time  for 
the  precipitation  of  0.2  gram  of  the  combined  metals. 
Under  iron  from  cobalt  mention  was  made  of  a 
method  which  can  be  pursued  in  separating  the  metals 
now  under  discussion.  To  repeat,  it  consists  in  oxidiz- 
ing the  iron  with  bromine,  then  introducing  into  the 
solution  from  3  to  6  grams  of  ammonium  sulphate  and 
a  moderate  excess  of  ammonium  hydroxide.  From 
this  solution  the  nickel  will  be  deposited  in  from  2  to  3 
hours,  with  a  current  of  N.D100  =  0.4-0.8  ampere.  As 
in  the  case  of  the  cobalt,  traces  of  iron  will  appear  in  the 
nickel.  This  occlusion,  so  to  speak,  of  iron  has  become 
a  subject  of  discussion  among  those  using  electro- 
lytic methods.  Neumann  (Ch.  Z.,  22,  731)  remarks 
that  it  has  tacitly  been  understood  that  the  nickel  car- 
ries down  no  iron  with  it.  Indeed,  Engels  (Thesis, 
Bern)  claims  to  have  obtained  perfectly  correct  results. 
Vortmann,  as  indicated,  and  also  Ducru  (Ch.  Z.,  21, 
780;  C.  r.,  125,  436;  B.  s.  Ch.  Paris,  17,  1881)  recom- 
mend the  solution  of  the  nickel  and  the  determination 
of  any  iron  present.  So  well  satisfied  is  Ducru  that  he 
employs  this  method  for  the  estimation  of  nickel  in 
steel,  asserting  that  the  amount  of  enclosed  iron  is  fairly 
constant  (varying  between  i  and  2  mg.),  and  that  for 


SEPARATION    OF    METALS IRON.  187 

technical  or  commercial  purposes  it  may  be  ignored. 
Neumann,  on  the  other  hand,  maintains  the  abso- 
lute necessity  of  determining  the  amount  of  iron  co- 
precipitated.  In  the  analysis  of  nickel  steel  and  nickel 
matte  he  proceeds  as  follows : — 

Dissolve  the  substance  in  dilute  sulphuric  acid,  and 
after  a  brief  period  introduce  hydrogen  peroxide  into 
the  solution  to  oxidize  the  carbon  and  the  iron,  thus 
obtaining  a  clear,  yellow  solution.  Now  add  ammo- 
nium sulphate  and  ammonia,  boil  and  continue  the  addi- 
tion of  ammonia  to  an  excess,  then  dilute  to  a  definite 
volume.  Filter  out  100  c.c.  of  this  solution,  mix  with 
it  ammonium  sulphate  and  ammonia,  dilute  to  175- 
200  c.c.,  and  electrolyze  the  hot  liquid  with  N.Dloo  = 
1-2  amperes  and  3.4-3.8  volts.  The  electrolysis  will 
be  finished  at  the  expiration  of  from  i  J  to  2  hours. 

For  another  method  by  Vortmann  applicable  here, 
see  zinc  from  nickel  in  the  presence  of  Rochelle  salt 

P-  189). 

6.  From  Phosphoric  Acid.     If  the  iron  has  been  precipi- 
tated from   an   oxalate   solution   (p.  99),  from  a   ci- 
trate solution,  or  from  an  ammoniacal   tartrate  solu- 
tion, the  liquids  poured  off  from  the  iron  deposit  will  con- 
tain the  phosphoric  acid,  which  can  then  be  removed 
as  ammonium  magnesium  phosphate. 

7.  From  Titanium.     The  method  described  on  p.    ico, 
with  the  conditions  given  there,  will  answer  perfectly 
in  making  this  separation. 

8.  From    Uranium.       (Ber.,    14,    2771;    18,    2483.)      In 
making  this  separation,  follow  the  directions  outlined 
on  p.  99  for  the  separation  of  iron   from  aluminium. 
The  uranium  is  precipitated  in  the  form  of  hydroxide. 

9.  From  Zinc.     Add  to  the  solution  of  the  metals  1-3 


I  88  ELECTRO-CHEMICAL    ANALYSIS. 

c.c.  of  a  solution  of  potassium  oxalate  (i :  3)  and  3  to  4 
grams  of  ammonium  oxalate  and  electrolyze  the  liquid 
with  a  current  of  N.D100  ==  i  to  1.2  amperes.  The  zinc 
is  deposited  first,  and  no  difficulty  is  experienced,  pro- 
viding its  quantity  is  less  than  one-third  that  of  the  iron 
present.  Classen  provides  for  this  condition  by  adding 
a  weighed  amount  of  pure  ferrous  ammonium  sulphate 
in  excess.  Vortmann  (M.  f.  Ch.,  14,  536)  suggests  two 
methods : — 

(a)  Add    potassium  cyanide  to  the  solution  of  the 
metals  until  the  precipitate  formed  at  first  has  dissolved , 
then  introduce  sodium  hydroxide.     The  iron  is  present 
in  the  solution  as  ferrocyanide,  which  in  the  presence 
of  free  alkali  is  not  decomposed  by  the  current.     Avoid 
too  large  an  excess  of  potassium  cyanide,  as  it  retards 
the   separation   of  the   zinc.     The  current   should   be 
N.D100  =  0.3-0.6  ampere. 

(b)  Several  grams  of   Rochelle  salt  are  introduced 
into  the  solution  of  the  metals  and  then  an  excess  of 
10-20  per  cent,  sodium  hydroxide,  after  which  the  elec- 
trolysis is  conducted  at  5o°-6o°  with  a  current  of  N.D100 

=  0.07-0.1  ampere  and  an  electrode  pressure  of  2  volts. 

1.  Cobalt  from  Manganese.     The  course  generally  recom- 
mended for  this  separation  is  precisely  like  that  given 
for  the  separation  of  iron  from  manganese.     Owing  to 
the  great  tendency  of  the  manganese,  toward  the  close 
of  the  decomposition,  to  separate  out  as  dioxide  which 
settles  on  the  cobalt  deposit,  the  method   can   hardly 
be  regarded  as  being  accurate. 

2.  From  Nickel.     To  the  acetic  acid  solution  of  the  metals 
add  3    grams    of    ammonium  sulphocyanide,   i   gram 
of  urea,  and  from   i  to   2   c.c.  of  ammonia  water   to 


SEPARATION    OF    METALS — NICKEL,  ZINC.  189 

neutralize  the  excess  of  acid.  Warm  the  solution  to 
7o°-8o°,  and  electrolyze  with  a  current  of  N.Dloo  =  0.8 
ampere  and  i  volt.  The  time  of  precipitation  is  one 
and  one-half  hours.  Nickel  and  sulphur  pass  to  the 
anode,  while  the  cobalt  remains  unprecipitated.  The 
nickel  should  be  dissolved  in  acid  and  reprecipitated 
according  to  the  method  described  on  p.  91,  to  obtain 
it  pure.  The  liquid  poured  off  from  the  first  nickel  de- 
posit should  be  evaporated  to  dryness  several  times 
with  nitric  acid,  the  residue  taken  up  in  water,  and  the 
solution  treated  as  directed  on  p.  93  (Balachowsky, 
C.  r.,  132,  1492;  also  M.  f.  Ch.,  14,  548). 
3.  From  Zinc.  Add  several  grams  of  Rochelle  salt 
and  an  excess  of  a  dilute  sodium  hydroxide  solu- 
tion to  the  liquid  containing  the  metals.  Warm  to  65° 
and  electrolyze  with  N.D100  =  0.3-0.6  ampere  and  2 
volts.  Usually  there  is  a  deposit  upon  the  anode,  hence 
it  is  advisable  to  previously  weigh  the  latter  and  again 
at  110°  after  the  precipitation  is  complete  (Elektroch. 
Z.,  1,  7). 

1.  Nickel  from  Manganese.     What  was  said  of  the  separa- 
tion of  cobalt  from  manganese  applies  here  in  every 
particular. 

2.  From    Zinc.      Add   4   to    6   grams   of    Rochelle   salt 
to  the  solution  of  the  two  metals,  then  a  concentrated 
solution  of  sodium  hydroxide.     Electrolyze  the  mix- 
ture with  a  current  of  N.  D100  ==  0.3-0.6  ampere.     The 
precipitation  of  the  zinc  will  be  finished  in  a  period  of 
from  2  to  4  hours.     Pour  off  the  alkaline  licjuid,  wash 
the  zinc  deposit  with  water  and  alcohol;  dry  at  100°  C. 

1.  Zinc  from  Manganese.     A  solution  contained  0.5074 


ELECTRO-CHEMICAL    ANALYSIS. 

gram  of  zinc  sulphate  and  0.1634  gram  of  manganese 
sulphate.  To  it  were  added  5  grams  of  ammonium 
lactate,  0.75  gram  of  lactic  acid,  and  2  grams  of  ammo- 
nium sulphate.  It  was  diluted  to  200  c.c.  and  electro- 
lyzed  at  2o°-25°  C.  with  a  current  of  N.D100  =  0.24-0.26 
ampere  and  3.7-3.9  volts.  In  4  hours  22.786  per  cent, 
of  zinc  was  found,  while  theory  required  22.78  per  cent. 
(Riderer,  J.  Am.  Ch.  $.,  27,789). 

The  writer  would  recommend  the  following  course  in 
separating  the  metals  of  this  group:  Separate  the  iron 
from  the  manganese,  zinc,  nickel,  and  cobalt,  by  precipi- 
tation with  barium  carbonate.  Dissolve  the  iron  precip- 
itate in  citric  acid,  and  electrolyze  the  solution  according 
to  the  directions  given  upon  p.  100.  The  filtrate,  con- 
taining the  zinc,  manganese,  nickel,  and  cobalt,  together 
with  a  little  barium  salt,  is  carefully  treated  with  just 
sufficient  dilute  sulphuric  acid  to  remove  the  barium. 
After  filtering,  electrolyze  the  filtrate  in  a  platinum  dish, 
connected  with  the  anode  of  a  battery,  with  a  cur- 
rent of  0.3-0.5  ampere.  A  weighed  piece  of  platinum 
foil  will  answer  for  the  cathode.  The  manganese  is 
deposited  as  dioxide  (p.  96);  the  other  metals  remain 
dissolved  and  can  only  be  separated  by  one  of  the  usual 
gravimetric  methods;  or  perhaps  the  suggestion  of  Vort- 
mann  (p.  189),  for  the  separation  of  zinc  from  nickel  and 
cobalt,  would  be  applicable  here,  and  these  two  might 
then  be  separated  as  outlined  on  p.  189.  This  course 
proved  quite  satisfactory  in  the  analysis  of  the  mineral 
franklinite,  where,  after  having  obtained  the  iron  and 
manganese  as  described,  the  zinc  was  also  determined 
electrolytically  in  the  liquid  poured  off  from  the  man- 
ganese deposit.  If  the  solution  containing  these  two 


SEPARATION    OF    METALS URANIUM.  19! 

metals  be  very  slightly  acid  with  sulphuric  acid,  they  can 
be  precipitated  simultaneously — the  zinc  at  the  cathode, 
and  manganese  dioxide  at  the  anode. 


URANIUM. 

Smith  has  called  attention  to  the  separation  of  uranium 
in  the  electrolytic  way  from  the  alkali  metals  and  from 
barium  (p.  102).  Actual  results  are  given.  It  seemed 
desirable  to  amplify  the  suggestion;  hence  the  presenta- 
tion of  the  results  given  below.  It  may  be  said  here, 
that  in  attempting  to  separate  uranium  from  nickel  and 
cobalt  no  satisfaction  could  be  obtained,  so  that  even- 
tually that  particular  line  of  experiment  was  abandoned. 
During  the  precipitation  of  the  urano-uranic  hydrate  the 
dish  should  be  well  covered  so  that  as  little  evapora- 
tion as  possible  occurs.  It  was  observed  that  in  case  of 
evaporation  there  was  danger  of  other  salts  separating 
upon  the  exposed  metal,  and  on  refilling  with  water  the 
uranium  precipitate  was  apt  to  enclose  the  same  and  thus 
carry  with  it  a  slight  impurity.  This  precaution  is  espe- 
cially necessary  in  the  separation  from  zinc  (J.  Am.  Ch. 
S.,  23,  608). 

I.  FROM  BARIUM  (ACETATES). 


z 

H 

z 

So 

U 

U 
o 

z 

w 

z 

!xl     • 
VI  W 

k  . 

U 

U 

u 

Q" 

a! 

c/i  5 

£« 

g  < 

OH    0! 

z  u 

z 

0 

D 
H 

z 

u 

Qj 

t/i 

H 

0 

ffi 

I" 

0 
Z 

(X  « 

«  O 

ri 

K 

0 

P^ 

>"H 

6° 

D  Z 

a  P 

D 

j 

(i) 
0. 

D 
U 

> 

u 

0° 

o 

^  u 

Q 

a 

h 

i 

D 

PQ 

$< 

h 

W 

O.III6 

0.  II 

0.5 

I2.S 

70 

N.D]07  =  0.02  A 

2 

51 

O.III9 

-(-0.0003 

o.  1116 

O.I  I 

o-.S 

I2.S 

615 

N.D107  =  0.04  A 

8 

Si 

O.III7 

-(-O.OOOI 

0.1116 

0.  II 

0.2 

125 

70 

N.D107^o.i    A 

4-5 

4 

O.III7 

+  O.OOOI 

192 


ELECTRO-CHEMICAL   ANALYSIS. 


2.  FROM  CALCIUM  (ACETATES). 


z 

£ 

So 

M 

^ 

OT 

f-1 

a 

f     ^ 

t/5 

*"' 

s 

z 

M     W 

ti« 

U 

a 

• 

Q 

< 

«i 

£S 

o*  2 

h'S 

Z  U 

z' 

(6 

|3 

H 

u 

g 

0 

3 

|i 

0 

£  ol 

u  .. 

o 

< 

os 

0 

£2 

z 

O 

^  >?• 

P 

W 

K* 

a 

ooO 

^ 

r-N 

P 

OH 

U 

g 

o 

^ 

< 
u 

^ 

Q 

W 

H 

H 

D 

OS 

OS 

U 

0.1116 

O.  I 

O.2 

125 

70 

N.D107  =  0.025  A 

2.25 

6£ 

o  1113 

—  O.OOO3 

o.  ii  1  6 

O.I 

0.2 

125 

70 

N.D107  =  o.O4    A 

2.2 

S* 

0.1114 

—  O  OOO2 

o.  1116 
0.1116 

O.I 
O.I 

O.  2 
0.2 

125 
125 

70 
70 

N.D107  =  0.05    A 
N.D107  =  0.025  A 

2.25 
2.0 

4f 

0.1113 
0.1115 

—  O.OOO3 
O.OOOI 

3.   FROM  MAGNESIUM  (ACETATES). 


Z 

J)  . 

[I]  t/3 

[z]     . 
K  U 

u 

o 

z 

w 

z 

OS   S 

OH   < 

h° 

U 

u 

[J 

t/5 

Q" 

< 

U  </) 

go 

h  Q' 

z  n 

z 

a; 
D 

Z 

W 

[2 

D 
0 

5,g' 

O 

as  < 

Bz 

5< 

0 

H 
< 

j 

o 

re 

fe  « 

z 

^  C5 

[z] 

uu 

i-| 

OS 

Jj 

> 

[ii 

oorjj 

- 

(5" 

z  H" 

o  z 

wS 

J 

a 

OH 

u 

s 

°? 

0 

u5 

<  a 

ft.  8 

Q 

a 

H 

P 

^ 

S 

^< 

H 

w 

o.  1116 

O.I 

O.I 

125 

70 

N.D107=r  0.026  A 

2.25 

6 

o.  1  1  1  5 

—  O.OOOI 

O.  IIO2 

O.I 

O.I 

125 

70 

N.D107=o.o5    A 

2.25 

5} 

0.1104 

4-O.OOO2 

o.  n  20 

O.I 

O.I 

125 

75 

N.D107  =  o.i5    A 

4.0 

4 

o.  1119 

—  O.OOOI 

4.  FROM  ZINC  (ACETATES). 


Z 

M     • 

z 

iu 

u 

o* 

t/3 

z 

i/5 

H 
Z 

H 
Z    . 

b;  t/3 

h'9 

U 

a 

OS 

h 

OS 
D 

O 

o" 
g  </> 

as 
O 

a  S 

i< 

z' 

0 

D 
H 

w 

S 

a 

o^ 

Z 

0.  OS 

os  oS 

U  u 

p 

OS 

OS 

^ 

. 

ta  & 

„ 

(5 

U 

OS  U 

a  $ 

2 

OH 

U 

g 

o'J 

as 
O 

Z 

OH    U 

Q 

g 

^ 

^ 

a: 

OS 

p 

N 

^ 

a 
H 

W 

0.  I  I  20 

O.I 

O.I 

125 

70 

N.D107=,o.o2IA 

2.25 

6 

0.  1  1  2O 

O.II02 

0.2 

O.2 

125 

70 

N.Djo7=:  0.017  A 

2.25 

6 

0.1099 

—  0.0003 

O.IIO2 

O.  I 

O.I 

125 

70 

N.D107  =  oo2    A 

2.2 

6 

O.  IIOO 

—  O.OOO2 

O.  IIO2 

O.I 

O.I 

125 

75 

N.D107  =  0.025  A 

4.4 

4* 

0.1103 

-f-O.OOOI 

O  1  102 

0.15 

O.2 

I25 

75 

N.D]07=o.oi    A 

2.2 

6 

0.1105 

+0.0003 

O.IIO2 

O.2 

O.  2 

125 

75 

N.D107=:0.02    A 

2.25 

6 

o.  1099 

—0.0003 

DETERMINATION    OF    THE    HALOGENS.  193 


3.  DETERMINATION  OF  THE  HALO- 
GENS   IN    THE    ELECTROLYTIC    WAY. 

LITERATURE. — Whitfield,  Am.  Ch.  Jr.,  8,  421  ;  Vortmann,  Elektroch. 
Z.,  i,  137;  2,  169. 

Whitfield  proceeds  as  follows :  The  silver  halide  is  col- 
lected in  a  Gooch  crucible  and  dried  directly  over  a  low 
Bunsen  flame.  After  weighing  it  is  dissolved  by  intro- 
ducing the  crucible  and  asbestos  into  a  concentrated 
potassium  cyanide  solution.  The  silver  is  then  deposited 
in  a  platinum  dish  of  100  cm2  surface  with  a  current  of 
0.07  ampere.  It  is  not  advisable  to  work  with  more  than 
2  grams  of  silver  halide. 

Vortmann  has  developed  an  electrolytic  scheme  for  the 
direct  determination  of  the  halogens.  As  he  has  given 
the  most  attention  to  iodine,  its  method  of  estimation  will 
be  presented  here. 

To  the  aqueous  solution  of  potassium  iodide  were  added 
several  grams  of  Seignette  salt  and  16-20  c.c.  of  a  10  per 
cent,  solution  of  sodium  hydroxide.  The  liquid  was  then 
diluted  to  150  c.c.  and  placed  in  a  crystallizing  dish  or  in 
a  platinum  dish.  If  the  first  was  used,  then  a  platinum 
disc,  5  cm.  in  diameter,  was  made  the  cathode,  whereas 
in  the  second  instance  the  dish  itself  became  the  cathode, 
the  anode  being  a  circular  plate  of  pure  silver,  5  cm.  in. 
diameter,  or  a  plate  of  platinum  of  like  size,  coated  with 
silver.  The  electrolysis  was  made  with  a  current  of  0.03- 
0.07  ampere  and  2  volts.  It  was  found  expedient,  after 
several  hours,  to  replace  the  anode  coated  with  silver 
iodide  with  another,  and  the  electrolysis  was  continued 
17 


194  ELECTRO-CHEMICAL    ANALYSIS. 

until  the  anode  ceased  to  increase  in  weight.  This  change 
in  anodes  is  absolutely  necessary  when  the  quantity  of 
iodine  exceeds  0.2  gram.  The  iodine  may  exist  as  iodide 
or  iodate.  The  alkaline  tartrate  is  introduced  to  prevent 
the  silver  iodide  from  becoming  detached. 


4.    DETERMINATION    OF    NITRIC    ACID 
IN   THE    ELECTROLYTIC   WAY. 

LITERATURE. — Vortmann  ,  Ber.,  23,  2798. 

To  the  solution  of  the  nitrate,  in  a  platinum  dish,  add  a 
sufficient  quantity  of  copper  sulphate.  Acidulate  the 
liquid  with  dilute  sulphuric  acid  and  electrolyze  with  a 
current  of  o.  i  to  0.2  ampere.  When  the  deposition  of  the 
copper  is  completed,  pour  off  the  liquid,  reduce  it  to  a 
small  volume,  and  distil  off  the  ammonia  in  the  usual 
manner.  The  quantity  of  copper  sulphate  added  should 
be  determined  by  the  quantity  of  nitric  acid  present.  If 
potassium  nitrate  is  the  salt  undergoing  analysis,  add 
half  of  its  weight  in  copper  sulphate. 


5.    OXIDATIONS   BY   MEANS   OF   THE 
ELECTRIC   CURRENT. 

LITERATURE. — Smith,  Ber.,  23,  2276;  Am.  Ch.  Jr.,  13,414;  Frankel, 
Ch.  News,  65,  64. 

When  natural  sulphides,  e.  g.,  chalcopyrite,  marcasite, 
etc.,  are  exposed  to  the  action  of  a  strong  current  in  the 
presence  of  a  sufficient  quantity  of  potassium  hydroxide, 
their  sulphur  will  be  quickly  and  fully  oxidized  to  sul- 


OXIDATIONS    BY    CURRENT.  195 

phuric  acid  (Jr.  Fr.  Ins.,  April,  1889;  Ber.,  22,  1019). 
The  metals  (iron,  copper,  etc.)  originally  present  in  the 
mineral  separate  as  oxides  and  metal  on  dissolving  the 
fused  alkaline  mass  in  water.  This  method  of  oxidation 
eliminates  many  other  disagreeable  features  of  the  old 
methods.  Its  rapidity  and  accuracy  entitle  it  to  the  fol- 
lowing brief  description: — 

Place  about  20  grams  of  caustic  potash  in  a  nickel 
crucible  ij  inches  high  and  if  inches  wide.  Apply  heat 
from  a  Bunsen  burner  until  the  water  has  been  almost  en- 
tirely expelled,  when  the  flame  is  lowered  so  that  the  tem- 
perature is  just  sufficient  to  retain  the  alkali  in  a  liquid 
condition.  The  crucible  is  next  connected  with  the  nega- 
tive pole  of  a  battery,  and  the  sulphide  to  be  oxidized  is 
placed  upon  the  fused  alkali.  As  some  natural  sulphides 
part  with  a  portion  of  their  sulphur  at  a  comparatively 
low  temperature,  it  is  advisable  to  allow  the  alkali  to  cool 
so  far  that  a  scum  forms  over  its  surface  before  adding  the 
weighed  mineral. 

The  heavy  platinum  wire,  attached  to  the  anode,  ex- 
tends a  short  distance  below  the  surface  of  the  fused  mass. 
When  the  current  passes,  a  lively  action  ensues,  accom- 
panied with  some  spattering.  To  prevent  loss  from  this 
source,  always  place  a  perforated  watch  crystal  over  the 
crucible.  After  the  current  has  acted  for  10-20  minutes, 
interrupt  it.  When  the  crucible  and  its  contents  are  cold, 
place  them  in  about  200  c.c.  of  water,  to  dissolve  out  the 
excess  of  alkali  and  alkaline  sulphate.  Filter.  Invaria- 
bly examine  the  residue  for  sulphur  by  dissolving  it  in 
nitric  acid  and  then  testing  with  barium  chloride.  The 
alkaline  filtrate  is  carefully  acidulated  with  hydrochloric 
acid,  and  after  digesting  for  some  time  is  precipitated  with 
a  boiling  solution  of  barium  chloride.  When  the  hydro- 


196  ELECTRO-CHEMICAL    ANALYSIS. 

chloric  acid  is  first  added,  care  should  be  taken  to  observe 
whether  hydrogen  sulphide  or  sulphur  dioxide  is  liberated. 
If  the  oxidation  is  incomplete  sulphur  also  makes  its  ap- 
pearance as  a  white  turbidity.  The  caustic  potash  em- 
ployed in  these  oxidations  should  always  be  examined  for 
sulphur  and  other  impurities.  As  it  is  difficult  to  obtain 
alkali  perfectly  free  from  sulphur  compounds,  a  weighed 
portion  should  be  taken  and  its  quantity  of  sulphur  de- 
ducted from  that  actually  found  in  the  analysis. 

The  arrangement  of  apparatus  employed  in  the  oxida- 
tions just  outlined  is  represented  in  Fig.  39.  The  crucible  A 
is  supported  by  a  stout  copper  wire  bent  as  indicated,  and 
held  in  position  by  a  binding  screw  attached  to  the  base  of  a 
filter  stand.  The  arm  of  the  latter  carries  a  second  bind- 
ing screw  holding  the  platinum  anode  in  position.  While 
the  platinum  rod  is  generally  the  positive  electrode,  it  is 
best  to  make  it  the  negative  pole  for  at  least  a  part  of  the 
time  during  which  the  current  acts.  This  is  advisable 
because  in  many  of  the  decompositions  metals  are  pre- 
cipitated upon  the  sides  of  the  crucibles,  and  can  readily 
enclose  unattacked  sulphide,  so  that  by  reversing  the 
current  (the  poles)  any  precipitated  metal  will  be  de- 
tached, and  the  enclosed  sulphide  be  again  brought  into 
the  field  of  oxidation.  Cinnabar  is  a  sulphide  which  has  a 
tendency  to  mass  together,  and  it  could  only  be  decom- 
posed and  its  sulphur  thoroughly  oxidized  by  reversing 
the  current  every  few  minutes.  To  reverse  the  current 
use  the  contrivance  C;  this  is  nothing  more  than  a  square 
block  of  wood  fastened  to  the  top  of  the  table,  T,  by  a 
screw  or  nail.  The  four  depressions  (x)  in  it  contain  a  few 
drops  of  mercury,  into  which  the  side  binding  screws  (a) 
project.  The  mercury  cups  are  made  to  communicate 
with  each  other  by  a  cap  of  wood,  D,  carrying  two 


OXIDATIONS    BY    CURRENT. 


'97 


198  ELECTRO-CHEMICAL   ANALYSIS. 

wires,  which  pass  through  it  and  project  a  slight  distance 
on  its  lower  side.  By  raising  the  cap  and  turning  it  so  that 
the  wires  are  vertical  (-J-)  or  horizontal  ( — ^),  the  crucible 
or  the  platinum  wire  extending  into  the  fused  mass  can  be 
made  the  anode  or  cathode  in  a  few  seconds.  E  is  a  Kohl- 
rausch  amperemeter  (Fig.  20)  and  R  the  resistance  frame 
(Fig.  18). 

Storage  batteries  furnish  the  most  satisfactory  current 
for  work  of  this  character.  In  the  sketch  the  cells  stand 
beneath  the  table ;  the  wire  from  the  anode  passes  through 
a  hole  in  the  table-top,  and  is  attached  to  one  of  the  bind- 
ing-posts of  the  block  C,  while  the  positive  wire  is  attached 
to  a  binding-post  at  the  end  of  the  table-top,  and  from 
here  it  passes  to  the  resistance  frame,  R,  where  it  is  fixed 
by  an  ordinary  metallic  clamp. 

For  most  purposes  the  strength  of  current  need  not 
exceed  1-1.5  amperes;  however,  it  may  be  necessary 
occasionally  to  increase  it  to  4  amperes.  Pyrite,  FeS2, 
is  even  then  not  completely  decomposed.  This  particu- 
lar case  requires  the  addition  of  a  quantity  of  cupric 
oxide  equal  in  weight  to  the  pyrite  and  a  current  of  the 
strength  last  indicated  before  all  of  its  sulphur  is  fully  con- 
verted into  sulphuric  acid. 

By  increasing  the  number  of  crucibles  it  will  be  possible 
to  conduct  at  least  from  four  to  six  of  these  decompositions 
simultaneously,  and  by  using  a  volumetric  method  of 
estimating  the  sulphuric  acid,  a  sulphur  determination 
can  easily  be  executed  in  forty  minutes. 

Experience  has  demonstrated  that  0.1-0.2  gram  of 
material  will  require  about  20-25  grams  of  caustic  potash. 

Dr.  L/ee  K.  Frankel  has  conclusively  demonstrated  that 
the  arsenic  contained  in  metallic  arsenides,  e.  g.,  arsenopy- 
rite,  rammelsbergite,  etc.,  can  be  entirely  converted  into 


OXIDATIONS    BY    CURRENT.  199 

arsenic  acid  by  the  above  method.  He  recommends  con- 
ditions analogous  to  those  employed  with  the  sulphides. 
The  current  will  also  completely  decompose  the  mineral 
chromite.  For  a  quantity  of  material  varying  from  o.i- 
0.5  gram  use  from  30-40  grams  of  stick  potash  and  a  cru- 
cible slightly  larger  than  that  recommended  in  the  oxida- 
tion of  sulphides  and  arsenides.  The  current  should  not 
exceed  one  ampere.  Thirty  minutes  will  be  sufficient  for 
the  oxidation.  At  the  expiration  of  this  period  allow  the 
mass  to  cool,  take  up  in  water,  filter  off  from  the  iron  oxide, 
acidulate  the  nitrate  with  sulphuric  acid,  add  a  weighed 
quantity  of  ferrous  ammonium  sulphate,  and  determine 
the  excess  of  iron  with  a  standardized  bichromate  solution, 
using  potassium  ferricyanide  as  an  indicator.  Upon 
oxidizing  0.4787  gram  of  chromite  by  the  above  process 
51.77  per  cent,  of  chromic  oxide  was  obtained,  while  a  sec- 
ond sample  of  the  same  mineral,  oxidized  by  the  Dittmar 
method,  gave  51.70  per  cent,  of  chromic  oxide.  If  the 
chromium  be  estimated  volumetrically,  the  chromium 
content  in  a  chrome  ore  may  be  ascertained  in  less  than 
an  hour. 


INDEX. 


ACCUMULATOR,  23-25 

J\  A  1   -? 

Ampere,  13 

Amperemeter,  32,  33,  34 
Anions,  9 
Anode,  9 
Antimony,  determination  of,    115- 

119 

separation  from  arsenic,  177 
bismuth,  156 
copper,  121,  122 
lead,   164 
mercury,  147 
silver,  168,  169 
tin,  177,  178,  179,  180,  181 
Arsenic,  determination  of,  120 
oxidation  of,  198 
separation  from  antimony,  177 
bismuth,  156 
cadmium,  138 
copper,   122,   123 
lead,   165 

mercury,   147,  148 
silver,   169 
tin,  181 


gATTERY,  Bunsen,  18 

Crowfoot,  16 
Cupron,  19 
Daniell,  16 
Grenet,  14 
Grove,    18 
Leclanche,  15 
Meidinger,   16 
storage,  23,  24,  25 
Bismuth,  determination  of,  75-78 
separation  from  aluminium,   156 

antimony,    156 

arsenic,  156 

barium,  157 

cadmium,  157 

18  : 


Bismuth,  separation  from  calcium, 
157 

chromium,   157 

cobalt,  158 

copper,  158 

gold,   159 

iron,  159,  160 

lead,   160 

magnesium,   161 

manganese,  161 

mercury,  161 

molybdenum,  161 

nickel,  161 

palladium  and  platinum,  161 

potassium,  162 

selenium,  162 

silver,  162 

sodium,  162 

strontium,   162 

tellurium,  162 

tin,  162 

tungsten,   163 

uranium,  163 

vanadium,  163 

zinc,  163 
Bunsen  cell,  18 


QADMIUM,  determination  of,  68- 

separation  from  aluminium,  137, 

138 

antimony,  138 
arsenic,  138 

barium,  strontium,  etc.,  139 
beryllium,  139 
bismuth,  139 
chromium,  139 
cobalt,  139 
copper,  139 
gold,  140 


202 


INDEX. 


Cadmium,    separation    from    iron, 
140 

lead,  140 

magnesium,  140 

manganese,   141 

mercury,  142 

molybdenum,  142 

nickel,  142 

osmium,  143 

selenium,   143 

silver,   143 

sodium,  143 

strontium,   143 

tellurium,  143 

tin,  143 

tungsten,   143 

uranium,  143 

vanadium,   144 

zinc,  144,  145,  146 
Cathions,  9 
Cathode,  9,  64,  66,  68 
Chromite,  oxidation  of,  199 
Cobalt,  determination  of,  91-95 
separation  from  bismuth,  158 

cadmium,  139 

ccpper,  126,  127 
iron,   184 
manganese,   188 
mercury,  150 
nickel,  188 
silver,  170 
zinc,  189 

Copper,  determination  of,  58-68 
separation  from  aluminium,  121 
antimony,  121,  122 
arsenic,   122,   123 
barium,    strontium,    magne- 
sium, etc.,  124 
bismuth,  124,  125 
cadmium,  124 
calcium,  126 
chromium,  126,  127 
gold,  127 

iron,  127,  128,  129 
lead,  129,  130 
magnesium,  130 
manganese,  131,  132 
mercury,  132 
molybdenum,  132 
nickel,  132,  133 
palladium,   133 
platinum,  133 
potassium,  133 


Copper,  separation  from  selenium, 

133 

silver,  134 
sodium,  133 
strontium,   133 
tellurium,  134 
thallium,  134 
tin,  134 
tungsten,   135 
uranium,  135 
vanadium,   135 
zinc,   135,   136,   137 
Crowfoot  cell,  16 
Cupron  cell,  19 

Current,  action  upon  compounds,  10 
density,  35 

electric  light,  25,  26,  27 
measuring  of,  32 
reduction  of,  28 

QANIELL  cell,  16 
Dynamos,  20 

ELECTRIC  current,  sources  of,  14 

light  current,  25-27 
motor,  76 

Electro-chemical  laboratory,  37-44 
Electrolysis,  defined,  9 
Electrolyte,  9 

QOLD,  determination  of,  111 

separation  from  antimony,  175 

arsenic,  176 

cobalt,  175 

copper,  175 

nickel,  175 

palladium,   175 

platinum,  176 

zinc,  176 
Grenet  cell,  14 
Grove  cell,  18 

UALOGENS,    determination     of, 

193 
Historical  account,  44-57 


]RON,  determination  of,  98-102 
separation     Irom     aluminium 

182,  183 
bismuth,   159,   160 


INDEX. 


203 


Iron,  separation  from  cadmium,  140 
chromium,  183 
cobalt,  189 
copper,  127,  128,  129 
lead,   165 
manganese,   184 
mercury,  151,  152 
nickel,   186,   187 
phosphoric  acid,  187 
silver,   172 
titanium,   187 
zinc,   187 


,  determination  of,  78-80 
separation  from   alkali  metals,   j 
barium,  beryllium,  cadmi- 
um, calcium,  cobalt,  iron, 
magnesium,    nickel,    ura- 
nium, zinc,  zirconium,  165 

aluminium,   164 

antimony,  164 

arsenic,  165 

bismuth,  166 

manganese,   166 

mercury,  166 

selenium,   167 

silver,   167 

tellurium,  168 

tin,  168 
Leclanche  cell,   15 


MAGNETO-MACHINES,  20 

Manganese,    determination    of, 

95-98 
separation  from  aluminium,  95 

bismuth,  161 

cadmium,  141 

cobalt,  188 

copper,  131,  132 

iron,   184 

mercury,  152 

nickel,  189 

zinc,   189 
Meidinger  cell,  16 
Mercury,  determination  of,  72-75 
separation  from  aluminium,   146 

antimony,  147 

arsenic,   147,   148 

barium,  strontium,  etc.,  148 

bismuth,   148,   149 

cadmium,  149 


Mercury,  separation  from  calcium, 
150 

chromium,  150 

cobalt,  150 

copper,    150,    151 

gold,  151 

iron,  151,  152 

lead,   152 

magnesium,  152 

manganese,   152 

molybdenum,    153 

nickel,  153 

osmium,  153 

palladium,   153 

platinum,  153 

potassium,  154 

silver,   154 

sodium,  154 

strontium,   154 

tellurium,  154 

tin,  154 

tungsten,  155 

uranium,   155 

vanadium,   155 

zinc,  155,  156 
Molybdenum,      determination     of, 

107-110 
separation  from  cadmium,  142 

mercury,  153 

silver,  173 


[SJICKEL,  determination  of,  91-95 
separation     from     aluminium, 
186 

bismuth,  161 

cadmium,  142 

cobalt,  139 

copper,  132,  133 

iron,  186,  187 

lead,   165 

manganese,    189 

mercury,  153 

silver,   173 

zinc,   189 

Nitric  acid,  determination  of,  194 
Normal  density  defined,  35 


QHM,  13 

Osmium,  48 

Oxidations  by  means  of  the  current, 
195 


204 


INDEX. 


PALLADIUM,    determination    of, 

106 
separation  from  iridium,  177 

mercury,  153 
Phosphoric    acid,    separation,   etc. 

183,  187 
Platinum,    determination    of,    104, 

105 

metals,   177 

separation  from  iridium,  177 
Potential  across  the  poles,  35 


RESISTANCE    coils  and  frames, 

28-31 
Rhodium,  determination  of,  107 


gILVER,  determination  of,  81-84 
separation     from      aluminium, 

168 

antimony,  168,  169 
arsenic,  169 
barium,  169 
bismuth,  169 
cadmium,  169 
calcium,   170 
chromium,   170 
cobalt,  170 
copper,  170,  171,  172 
gold,  172 
iron,   172 
lead,   172 
lithium,  172 
magnesium,  172 
manganese,   172 
mercury,    173 
molybdenum,    173 
nickel,  173 
palladium,  173 
platinum,  173 
potassium,  173 
selenium,   173 
tellurium,  173 
tin,  174 


Silver,    separation    from    uranium, 

174 

zinc,   174 

Sulphur,  oxidation  of,  195,  196,  197, 
198 

JANGENT,  galvanometer,  33 

Thallium,     determination     of, 

104 

Thermopile,  20-22 
Tin,  determination  of,   112-114 
separation  from  antimony,    177, 

178,  179,  180,  181 
arsenic,  181 
bismuth,  162 
cadmium,  143 
copper,  134 
lead,   168 
mercury,  154 


T  JRANIUM,  determination  of,  102- 

104 

separation  from  barium,  191 
calcium,   192 
magnesium,  192 
zinc,   192 

VOLT,  13 

Voltameter,  32,  58 
Voltmeter,  35 


2 INC,  determination  of,  84-91 
separation     from     aluminium, 

190 

bismuth,  163 
cadmium,  144,  145,  146 
copper,  135,  136,  137 
iron,   187 
lead,   165 
manganese,   189 
mercury,   155,   156 
silver,  174 


MEDICAL 
BOOKS 


There  have  been  sold  more  than 
145,000  copies  of  Gould's  Dictionaries 

See  Page  12 


P.   BLAKISTON'S  SON  &  COMPANY 
PUBLISHERS  OF  MEDICAL  AND  SCIENTIFIC  BOOKS 

1012  WALNUT  STREET,  PHILADELPHIA 


Montgomery's  Gynecology 

A   PRACTICAL  TEXT-BOOK 


A  modern  comprehensive  Text-Book.  By  EDWARD  E. 
MONTGOMERY,  M.D.,  Professor  of  Gynecology  in  Jefferson 
Medical  College,  Philadelphia;  Gynecologist  to  the  Jefferson 
and  St.  Joseph's  Hospitals,  etc.  527  Illustrations,  many  of 
which  are  from  original  sources.  800  pages.  Octavo. 

Cloth,  $5.00;  Leather,  $6.00 

*#*  This  is  a  systematic  modern  treatise  on  Diseases  of 
Women.  The  author's  aim  has  been  to  produce  a  book 
that  will  be  thorough  and  practical  in  every  particular.  The 
illustrations,  nearly  all  of  which  are  from  original  sources, 
have  for  the  most  part  been  drawn  by  special  artists  who, 
for  a  number  of  months,  devoted  their  sole  attention  to  this 
work. 

"  The  book  is  one  that  can  be  recommended  to  the  student,  to 
the  general  practitioner — who  must  sometimes  be  a  gynecologist  to 
a  certain  extent  whether  he  will  or  not — and  to  the  specialist,  as  an 
ideal  and  in  every  way  complete  work  on  the  gynecology  of 
to-day— a  practical  work  for  practical  workers."—  The  Jour- 
nal of  the  American  Medical  Association. 

Byford's  Gynecology 

Third  Revised  Edition 
A  MANVAL  FOR.  STUDENTS   AND   PHYSICIANS 


By  HENRY  T.  BYFORD,  M.D.,  Professor  of  Gynecology  and 
Clinical  Gynecology  in  the  College  of  Physicians  and  Sur- 
geons of  Chicago ;  Professor  of  Clinical  Gynecology, 
Women's  Medical  School  of  Northwestern  University,  and 
in  Post-Graduate  Medical  School,  etc.  Third  Edition,  En- 
larged. 363  Illustrations,  many  of  which  are  from  original 
drawings  and  several  of  which  are  Colored.  I2mo. 

Cloth,  $3.00 

"  As  a  book  to  help  the  student  to  quickly  review  what  ought 
to  be  gotten  up,  so  as  to  be  prepared  for  the  early  examination,  it  is  of 
great  service.  Such  a  book  would  also  make  a  most  excellent  text- 
book for  the  college  class  room."—  Virginia  Medical  Semi-Monthly, 
Richmond. 


By   JAMES   TYSON.   M.  D, 

Professor  of  Medicine,  University  of  Pennsylvania, 
Physician  to  the  Philadelphia  Hospital,  etc. 


The  Practice  of   Medicine.     Second  Edition. 

A  Text-Book  for  Physicians  and  Students,  with  Special  Ref- 
erence to  Diagnosis  and  Treatment.  With  Colored  Plates 
and  many  other  Illustrations.  Second  Edition,  Revised  and 
Enlarged.  127  Illustrations.  8vo.  1222  pages. 

Cloth,  $5.50;  Leather,  $6.50;  Half  Russia,  $7.50 
*#*  This  edition  has  been  entirely  reset  from  new  type. 
The  author  has  revised  it  carefully  and  thoroughly,    and 
added  much  new  material  and  37  new  illustrations. 

"  We  are  firmly  convinced  that  at  the  present  time  Dr.  Tyson's 
book  on  Practice  can  be  most  heartily  commended  to  both  the  practi- 
tioner and  student  as  a  safe,  reliable,  and  thoroughly  up-to-date  guide 
in  the  practice  of  medicine." — The  Therapeutic  Gazette. 

"  The  clinical  descriptions  are  clear  and  full,  and  the  methods  of 
treatment  described  are  those  generally  recognized  as  being  the  most 
modern  and  satisfactory." — The  London  Lancet. 

Guide  to  the  Examination  of   Urine.     Tenth 
Edition. 

For  the  Use  of  Physicians  and  Students.  With  Colored 
Plate  and  Numerous  Illustrations  Engraved  on  Wood. 
Tenth  Edition,  Revised,  Enlarged,  and  in  many  parts  entirely 
rewritten.  Cloth,  $1.50 

*^*  A   French  translation   of  this  book  has  been  pub- 
lished in  Paris. 

"  The  book  is  probably  more  widely  and  generally  known  and  ap- 
preciated than  any  of  its  similars  in  subject  and  scope." — New  York 
Medical  Journal. 

"The  book  is  a  reliable  one,  and  should  find  a  place  in  the  library 
of  every  practitioner  and  student  of  medicine." — Boston  Medical  and 
Surgical  Journal. 

Handbook  of  Physical  Diagnosis.     Fourth 
Edition. 

Revised  and  Enlarged.  With  two  Colored  Plates  and  55 
other  Illustrations.  298  pages.  I2mo.  Cloth,  $1.50 

"  Like  everything  else  emanating  from  this  distinguished  author 
this  little  book  is  replete  with  practical  information  from  beginning  to 
end." — The  Chicago  Medical  Recorder. 

"  The  author  approaches  his   subject  from   a  practical   point  of 
view  and  the  little  work  will  prove  a  good  friend  to   the   student." — 
The  American  Journal  of  the  Medical  Science*. 
3 


NEW  THIRD  EDITION— JUST  READY 

MORRIS'  ANATOMY 

Rewritten — Revised — Improved 
WITH  MANY  NEW  ILLUSTRATIONS 

Out  of  102  of  the  leading  medical  schools  60  recommend 
"  Morris."  It  contains  many  features  of  special  advantage 
to  students.  It  is  modern,  up-to-date  in  every  respect.  It 
has  been  carefully  revised,  the  articles  on  Osteology  and 
Nervous  System  having  been  rewritten.  Each  copy  con- 
tains the  colored  illustrations  and  a  Thumb  Index. 

Octavo.     With  846  Illustrations,  of  which  267  are 
printed  in  colors. 

CLOTH,  $6.00;  LEATHER.  $7.00 


"  The  ever-growing  popularity  of  the  book  with  teachers  and  stu- 
dents is  an  index  of  its  value,  and  it  may  safely  be  recommended  to  all 
interested." — From  The  Medical  Record,  New  York. 

"  Of  all  the  text-books  of  moderate  size  on  human  anatomy  in  the 
English  language,  Morris  is  undoubtedly  the  most  up-to-date  and  accu- 
rate."— From  '1 'he  Philadelphia  Medical  Journal. 


McMurrich — Embryology 

Just  Ready.    276  Illustrations 


A  Text-Book  for  Medical  Students.  By  J.  PLAYFAIR 
McMuRRlCH,  Professor  of  Anatomy,  Medical  Department, 
University  of  Michigan.  500  pages.  Cloth,  $3.00 


NINTH  EDITION 


POTTER'S  MATERIA  MEDICA, 
PHARMACY,  AND  THERAPEUTICS 


An  Exhaustive  Handbook 


Including  the  Action  of  Medicines,  Special  Therapeutics  of 
Disease,  Official  and  Practical  Pharmacy,  and  Minute  Direc- 
tions for  Prescription  Writing,  etc.  Including  over  650 
Prescriptions  and  Formulae.  By  SAMUEL  O.  L.  POTTER, 
M.A.,  M.D.,  M.R.C.P.  (Lond.),  formerly  Professor  of  the 
Principles  and  Practice  of  Medicine,  Cooper  Medical  Col- 
lege, San  Francisco  ;  Major  and  Brigade  Surgeon,  U.  S. 
Vol.  Ninth  Edition,  Revised  and  Enlarged.  8vo. 
With  Thumb  Index  in  each  copy. 

Cloth,  $5.00  ;   Leather,  $6.00 

*#*This  is  the  most  complete  and  trustworthy  book 
for  the  use  of  students  and  physicians.  Students  who  pur- 
chase it  will  find  it  to  contain  a  vast  deal  of  information  not 
in  the  usual  text- books  arranged  in  the  most  practical  man- 
ner for  facilitating  study  and  reference.  It  cannot  be  sur- 
passed as  a  physician's  working  book. 

WHITE  AND  WILCOX.  Materia  Medica, 
Pharmacy,  Pharmacology,  and  Thera- 
peutics. Fifth  Edition* 

A  Handbook  for  Students.  By  W.  HALE  WHITE,  M.D., 
F.R.C.P.,  etc.,  Physician  to,  and  Lecturer  on  Materia 
Medica  and  Therapeutics  at,  Guy's  Hospital,  etc.  Fifth 
American  Edition,  Revised  by  REYNOLD  W.  WILCOX, 
M  A  ,  M.D. ,  LL.D. ,  Professor  of  Clinical  Medicine  and  Thera- 
peutics at  the  New  York  Post- Graduate  Medical  School  and 
Hospital ;  Visiting  Physician,  St.  Mark's  Hospital ;  Assist- 
ant Visiting  Physician,  Bellevue  Hospital.  I2rno. 

Cloth,  $3.00;  Leather,  $3.50 


SUBJECT  INDEX. 


Gould's  Medical  Dictionaries,  - 
Morris*  Anatomy,  New  Edition, 
Compends  for  Students, 


Page  12 
Page  4 
Page  26 


SUBJECT.  PACK 

Alimentary  Canal  (see  Surgery)  23 
Anatomy  ..............................     7 

Anesthetics  ..........................  18 

Autopsies  (see  Pathology)  .....  20 

Bacteriology  (see  Pathology)..  20 
Bandaging  (see  Surgery)  ........  83 

Blood,  Examination  of  ..........  20 

Brain  ..................................     8 

Chemistry.     Physics  .............     8 

Children,  Diseases  of  ............  10 

Climatology  .........................  18 

Clinical  Charts  ......................  24 

Compends  .........................  26 

Consumption  (see  Lungs)  .......  15 

Cyclopedia  of  Medicine  .  ........  12 

Dentistry  .............................  1  1 

Diabetes  (see  Urin.  Organs)..  24 
Diagnosis  .............................  10 

Diagrams  (see  Anatomy)  .......     7 

Dictionaries,  Cyclopedias  ......  12 

Diet  and  Food  .....................  18 

Disinfection  ........................  15 

Dissectors  ............................     7 

Ear  ....................................  13 

Electricity  ...........................  13 

Embryology  .........................     7 

Emergencies  .........................  23 

Eye  .....................................  13 

Fevers  .................................  14 

Food  ......  .  .............................  18 

Formularies    .  .........     ,  ......      21 


Heart  ..................................  14 

Histology  .............................  14 

Hydrotherapy  .......................  18 

Hygiene  ...............................  15 

Hypnotism  ...........................     8 

Insanity  ..............................     8 

Intestines  .......................  —  22 

Latin,  Medical  (see  Miscella- 
neous and  Pharmacy)  ......  18,20 

Life  Insurance  .......................  18 

Lungs  ...........................      ...  15 

Massage  ...............................  16 

Materia  Medica....  ...  16 


SUBJECT.  PAGE 

Mechanotherapy 16 

Medical  Jurisprudence 17 

Mental  Therapeutics 8 

Microscopy — 17 

Milk  Analysis  (see  Chemistry)      8 

Miscellaneous  18 

Nervous  Diseases  18 

Nose.... •.......•••.•»•...•...»....«..««  24 

Nursing  ...............................  10 

Obstetrics.. 20 

Ophthalmology 13 

Organotherapy 18 

Osteology  (see  Anatomy) 7 

Pathology 20 

Pharmacy 20 

Physical  Diagnosis n 

Physical  Training 16 

Physiology  , 21 

Pneumotherapy 18 

Poisons  (see  Toxicology) 17 

Practice  of  Medicine 22 

Prescription  Books  (Pharm'y),  21 

Refraction  (see  Eye) 13 

Rest 18 

Sanitary  Science 15 

Skin 23 

Spectacles  (see  Eye) 13 

Spine  (see  Nervous  Diseases)  18 

Stomach. 22 

Students'  Compends 26 

Surgery  and  Surg'l  Diseases,  23 

Technological  Books 8 

Temperature  Charts 24 

Therapeutics 16 

Throat 24 

Toxicology 17 

Tumors  (see  Surgery) 23 

U.  S.  Pharmacopoeia 21 

Urinary  Organs 24 

Urine ............ .......i... ...........    24 

Venereal  Diseases 25 

Veterinary  Medicine 25 

Visiting  Lists,  Physicians'. 
(Send  for  Special  Circular.) 

Water  Analysis 15 

Women,  Diseases  of. 25 


Self-Examination  for  Medical  Students.  3500  Questions  on 
Medical  Subjects,  with  References  to  Standard  Works  in  which  the 
correct  replies  will  be  found.  Together  with  Questions  from  State 
Examining  Boards.  3d  Edition.  Paper  Cover,  10  cts. 


SUBJECT  CATALOGUE  OF  MEDICAL  BOOKS.  7 

SPECIAL,  NOTE.— The  prices  given  in  this  catalogue  are 
net,  no  discount  can  be  allowed  retail  purchasers  under  any  considera- 
tion. This  rule  has  been  established  in  order  that  everyone  will  be 
treated  alike,  a  general  reduction  in  former  prices  having  been  made  to 
meet  previous  retail  discounts.  Upon  receipt  of  the  advertised  price  any 
book  will  be  forwarded  by  mail  or  express,  all  charges  prepaid. 

ANATOMY.     EMBRYOLOGY. 

MORRIS.  Text-Book  of  Anatomy.  Third  Revised  and  Enlarged 
Edition.  846  Illustrations,  267  of  which  are  printed  in  colors.  Thumb 
Index  in  Each  Copy.  Cloth,  $6.00 ;  Leather,'  $7.00 

"  The  ever-growing  popularity  of  the  book  with  teachers  and  students 

is  an  index  of  its  value." — Medical  Record,  New  York. 

BROOMELL.  Anatomy  and  Histology  of  the  Human  Mouth 
and  Teeth.  2d  Edition,  Enlarged.  337  Illustrations.  Cloth,  $4  50 

CAMPBELL.  Dissection  Outlines.  Based  on  Morris'  Anatomy. 
2d  Edition.  .50 

DEAVER.  Surgical  Anatomy.  A  Treatise  on  Anatomy  in  its 
Application  to  Medicine  and  Surgery.  With  499  very  Handsome  full- 
page  Illustrations  Engraved  from  Original  Drawings  made  by  special 
Artists  from  dissections  prepared  for  the  purpose.  Three  Volumes. 
By  Subscription  only . 

Half  Morocco  or  Sheep,  $24.00;  Half  Russia,  $27.00 

GORDINIER.  Anatomy  of  the  Central  Nervous  System. 
With  271  Illustrations,  many  of  which  are  original.  Cloth,  $6.00 

HEATH.    Practical  Anatomy.    9th  Edition.    321  Illus.          $4.2 5 

HOLDEN.     Anatomy.    A  Manual  of  Dissections.    Revised  by  A. 
HHWSON,  M.D.,  Demonstrator  of  Anatomy,  Jefferson  Medical  College, 
Philadelphia.     320  handsome   Illustrations.     7th    Edition.     In  two 
compact  lame  Volumes.    850  Pages.    Large  New  Type. 
Vol.    I.     Scalp— Face— Orbit— Neck— Throat— Thorax— Upper  Ex- 
tremity. $1.50 
Vol.  II.    Abdomen — Perineum — Lower     Extremity — Brain — Eye — 
Ear — Mammary  Gland — Scrotum — Testes.               $I-5° 

HOLDEN.  Human  Osteology.  Comprising  a  Description  of  the 
Bones,  with  Colored  Delineations  of  the  Attachments  of  the  Muscles. 
The  General  and  Microscopical  Structure  of  Bone  and  its  Develop- 
ment. With  Lithographic  Plates  and  numerous  Illus.  8th  Ed.  $5.25 

HOLDEN.     Landmarks.    Medical  and  Surgical.    4th  Ed.  .75 

HUGHES  AND  KEITH.  Dissections.  With  527  Colored  Plates 
and  other  Illustrations.  In  three  Parts.  Just  Ready. 

I,  Upper  and  Lower  Extremity.  $3-°° 

II,  Abdomen — Thorax.  $3-°o 

III,  Head — Neck — Central  Nervous  System.  $3.00 

MACALISTER.  Human  Anatomy.  Systematic  and  Topograph- 
ical. 816  Illustrations.  Cloth,  $5.00 ;  Leather,  $6.00 

McMURRICH.  Embryology.  The  Development  of  the  Human 
Body.  276  Illustrations.  Just  Ready.  $3.00 

MARSHALL.  Physiological  Diagrams.  Eleven  Life-Size 
Colored  Diagrams  (each  seven  feet  by  three  feet  seven  inches). 
Designed  for  Demonstration  before  the  Class. 

In  Sheets,  Unmounted,  $40.00 ;  Backed  with  Muslin  and  Mounted 
on  Rollers,  $60.00 ;  Ditto,  Spring  Rollers,  in  Handsome  Walnut  Wall 
Map  Case,  $100.00;  Single  Plates — Sheets,  $5.00;  Mounted,  $7.50 
Explanatory  Key,  .50.  Purchaser  must  pay  freight  charges. 

MINOT.    Embryology.     Illustrated.    Just  Ready.  $4.50 

POTTER.  Compend  of  Anatomy,  Including  Visceral  Anatomy. 
6th  Ed.  16  Lith.  Plates  and  117  other  Illus.  .80  ;  Interleaved,  $1.00 

WILSON.    Anatomy,     nth  Edition.    429  Illus.,  26  Plates.      $5.00 
1-26  03. 


SUBJECT  CATALOGUE. 


BRAIN  AND  INSANITY  (see  also 
Nervous  Diseases). 

BLACKBURN.  A  Manual  of  Autopsies.  Designed  tor  the  Use 
of  Hospitals  for  the  Insane  and  other  Public  Institutions.  Ten  full- 
page  Plates  and  other  Illustrations.  $1.25 

CHASE.     General  Paresis.     Illustrated.    Just  Ready.  $1.73 

DERCUM.  Mental  Therapeutics,  Rest,  Suggestion.  See 
Cohen ,  Physiologic  Therapeutics,  page  /6. 

GORDIN IER.  The  Gross  and  Minute  Anatomy  of  the  Central 
Nervous  System.  With  full-page  and  other  Illustrations.  $6.00 

HORSLEY.  The  Brain  and  Spinal  Cord.  The  Structure  and 
Functions  of.  Numerous  Illustrations.  $2.50 

IRELAND.    The  Mental  Affections  of  Children.    2d  Ed.    $4.00 

LEWIS  (SEVAN).  Mental  Diseases.  A  Text-Book  Having 
Special  Reference  to  the  Pathological  Aspects  of  Insanity.  26  Litho- 
graphic Plates  and  other  Illustrations,  zd  Ed.  $7.00 

MANN.    Manual  of  Psychological  Medicine.  $3.00 

PERSHING.  Diagnosis  of  Nervous  and  Mental  Disease. 
Illustrated.  $1.25 

REGIS.  Mental  Medicine.  Authorized  Translation  by  H.  M. 
BANNISTER,  M.D.  $2.00 

SCHOFIELD.    The  Force  of  Mind.    Just  Ready.  $2.00 

STEARNS.  Mental  Diseases.  With  a  Digest  of  Laws  Relating 
to  Care  of  Insane.  Illustrated.  Cloth,  $2.75 ;  Sheep,  £3.25 

TUKE.  Dictionary  of  Psychological  Medicine.  Giving  the 
Definition,  Etymology,  and  Symptoms  of  the  Terms  used  in  Medical 
Psychology,  with  the  Symptoms,  Pathology,  and  Treatment  of  the 
Recognized  Forms  of  Mental  Disorders.  Two  volumes.  $10.00 

WOOD,  H.  C.    Brain  and  Overwork.  .40 

CHEMISTRY  AND  TECHNOLOGY. 

Special  Catalogue  of  Chemical  Books  sent  free  upon  application. 

ALLEN.    Commercial   Organic   Analysis.    A  Treatise  on  the 

Modes  of  Assaying  the  Various  Organic  Chemicals  and  Products 

Employed  in  the  Arts,  Manufactures,  Medicine,  etc.,  with  concise 

methods  for  the  Detection  of  Impurities,  Adulterations,  etc.    8vo. 

Vol.  I.  Alcohols,  Neutral  Alcoholic  Derivatives,  etc.,  Ethers,  Veg- 
etable Acids,  Starch,  Sugars,  etc.  3d  Edition.  $4.50 

Vol.  II,  Part  I.  Fixed  Oils  and  Fats,  Glycerol,  Explosives,  etc. 
3d  Edition.  $3-5<> 

Vol.  II,  Part  II.  Hydrocarbons,  Mineral  Oils,  Lubricants,  Benzenes, 
Naphthalenes  and  Derivatives,  Creosote,  Phenols, etc.  3d  Ed.  $3.50 

Vol.  II,  Part  III.  Terpenes,  Essential  Oils,  Resins,  Camphors,  etc. 
3d  Edition.  Preparing. 

Vol.  Ill,  Part  I.  Tannins,  Dyes  and  Coloring  Matters.  3d  Edition. 
Enlarged  and  Rewritten.  Illustrated.  $4-5° 

Vol.  Ill,  Part  II.  The  Amines,  Hydrazines  and  Derivatives, 
Pyridine  Bases.  The  Antipyretics,  etc.  Vegetable  Alkaloids,  Tea, 
Coffee,  Cocoa,  etc.  8vo.  ad  Edition.  $4-5° 

Vol.  Ill,  Part  III.  Vegetable  Alkaloids,  Non-Basic  Vegetable  Bitter 
Principles.  Animal  Bases,  Animal  Acids,  Cyanogen  Compounds, 
etc.  zd  Edition,  Svo.  $4-5° 

Vol.  IV.  The  Proteids  and  Albuminous  Principles,  zd  Ed.  $4.50 
BAILEY  AND  CADY.  Qualitative  Chemical  Analysis.  $1.25 


MEDICAL  BOOKS. 


HARTLEY.  Medical  and  Pharmaceutical  Chemistry.  A 
Text-Book  for  Medical,  Dental,  and  Pharmaceutical  Students.  With 
Illustrations,  Glossary,  and  Complete  Index.  5th  Edition.  $3.00 

HARTLEY.  Clinical  Chemistry.  The  Examination  of  Feces, 
Saliva,  Gastric  Juice,  Milk,  and  Urine.  $1.00 

BLOXAM.  Chemistry,  Inorganic  and  Organic.  With  Experi- 
ments, gth  Ed.,  Revised.  281  Engravings.  Preparing. 

BUNGB.  Physiologic  and  Pathologic  Chemistry.  From  the 
Fourth  German  Enlarged  Edition.  Just  Ready.  } 3.00 

CALDWELL.  Elements  of  Qualitative  and  Quantitative 
Chemical  Analysis.  3d  Edition,  Revised.  $1.00 

CAMERON.    Oils  and  Varnishes.    With  Illustrations.          $2.25 

CAMERON.     Soap  and  Candles.    54  Illustrations.  £2.00 

CLOWES  AND  COLEMAN.  Quantitative  Analysis.  5th 
Edition.  122  Illustrations.  $3-5o 

COBLENTZ.    Volumetric  Analysis.    Illustrated.  $1.25 

CONGDON.  Laboratory  Instructions  in  Chemistry.  With 
Numerous  Tables  and  56  Illustrations.  $1.00 

GARDNER.  The  Brewer,  Distiller,  and  Wine  Manufac- 
turer. Illustrated.  $1.50 

GRAY.  Physics.  Volume  I.  Dynamics  and  Properties  of  Matter. 
350  Illustrations.  $4-5o 

GROVES  AND  THORP.    Chemical  Technology.    The  Appli- 
cation of  Chemistry  to  the  Arts  and  Manufactures. 
Vol.  I.  Fuel  and  Its  Applications.     607  Illustrations  and  4  Plates. 

Cloth,  |s.oo;  >£  Mor.,  $6.50 

Vol.11.    Lighting.      Illustrated.  Cloth,  $4.00;  ^  Mor.,  $5.50 

Vol.  III.  Gas  Lighting.  Cloth,  ^3.50 ;  %  Mor.,  $4.50 

Vol.  IV.  Electric  Lighting.     Photometry.  In  Press. 

HEUSLER.     The  Terpenes.    Just  Ready.  £4.00 

HOLLAND.  The  Urine,  the  Gastric  Contents,  the  Common 
Poisons,  and  the  Milk.  Memoranda,  Chemical  and  Microscopi- 
cal, for  Laboratory  Use.  6th  Ed.  Illustrated  and  interleaved,  $1.00 

LEFFMANN.  Compend  of  Medical  Chemistry,  Inorganic 
and  Organic.  4th  Edition,  Revised.  .80;  Interleaved,  |i.oo 

LEFFMANN.      Analysis  of   Milk   and   Milk    Products.     2d 
Edition,  Enlarged.     Illustrated.  $i .25 

LEFFMANN.  Water  Analysis.  For  Sanitary  and  Technic  Pur- 
poses. Illustrated.  4th  Edition.  $1-25 

LEFFMANN.  Structural  Formulae.  Including  180  Structural 
and  Stereo-Chemical  Formulae.  i2mo.  Interleaved.  $1.00 

LEFPMANN  AND  BEAM.  Select  Methods  in  Food  Analy- 
sis. Illustrated.  $250 

MUTER.  Practical  and  Analytical  Chemistry.  2d  American 
from  the  Eighth  English  Edition.  Revised  to  meet  the  requirements 
of  American  Students.  56  Illustrations.  #1.25 

OETTEL.     Exercises  in  Electro-Chemistry.    Illustrated.       .75 

OETTEL.     Electro-Chemical  Experiments.    Illustrated.         .75 

RICHTER.  Inorganic  Chemistry.  $th  American  from  xoth  Ger- 
man Edition.  Authorized  translation  by  EDGAR  F.  SMITH,  M.A., 
PH.D.  89  Illustrations  and  a  Colored  Plate.  t*-75 

RICHTER.  Organic  Chemistry.  3d  American  Edition.  Trans, 
from  the  8th  German  by  EDGAR  F.  SMITH.  Illustrated,  a  Volumes. 
Vol.  I.  Aliphatic  Series.  625  Pages.  $3.00 

Vol.  II.    Carbocyclic  Series.    671  Pages.  $3.00 


10  SUBJECT  CATALOGUE. 

ROCK  WOOD.  Chemical  Analysis  for  Students  of  Medicine, 
Dentistry,  and  Pharmacy.  Illustrated.  $1-50 

SMITH.  Electro-Chemical  Analysis.  3d  Ed.  39  Illustrations. 
Just  Ready.  $  i .  50 

SMITH  AND  KELLER.  Experiments.  Arranged  for  Students 
in  General  Chemistry.  4th  Edition.  Illustrated.  .60 

SUTTON.  Volumetric  Analysis.  A  Systematic  Handbook  for 
the  Quantitative  Estimation  of  Chemical  Substances  by  Measure, 
Applied  to  Liquids,  Solids,  and  Gases.  8th  Edition,  Revised.  112 
Illustrations.  $5-°o 

SYMONDS.    Manual  of  Chemistry,    ad  Edition.  $2.00 

TRAUBE.  Physico-Chemical  Methods.  Translated  by  Hardin. 
97  Illustrations.  $1.50 

THRESH.    Water  and  Water  Supplies,    sd  Edition.          $2.00 

ULZER  AND  FRAENKEL.  Chemical  Technical  Analysis. 
Translated  by  Fleck.  Illustrated.  $1.25 

WOODY.  Essentials  of  Chemistry  and  Urinalysis.  4* 
Edition.  Illustrated.  $1.50 

%*  Special  Catalogue  of  Books  on  Chemistry  free  upon  application . 

CHILDREN. 

HATFIELD.  Compend  of  Diseases  of  Children.  With  a 
Colored  Plate.  3d  Edition.  Just  Ready.  .80;  Interleaved  |i.oo 

IRELAND.  The  Mental  Affections  of  Children.  Idiocy, 
Imbecility,  Insanity,  etc.  2d  Edition.  $4.00 

POWER.  Surgical  Diseases  of  Children  and  their  Treat- 
ment by  Modern  Methods.  Illustrated.  $2.50 

STARR.  The  Digestive  Organs  in  Childhood.  The  Diseases  of 
the  Digestive  Organs  in  Infancy  and  Childhood.  3d  Edition,  Rewrit- 
ten and  Enlarged.  Illustrated.  $3  °o 

STARR.  Hygiene  of  the  Nursery.  Including  the  General  Regi- 
men and  Feeding  of  Infants  and  Children,  and  the  Domestic  Manage- 
ment of  the  Ordinary  Emergencies  of  Early  Life,  Massage,  etc.  6th 
Edition.  25  Illustrations.  $1.00 

SMITH.    Wasting  Diseases  of  Children.    6th  Edition.        $2.00 

TAYLOR  AND  WELLS.  The  Diseases  of  Children.  2d  Edi- 
tion, Revised  and  Enlarged.  Illustrated.  8vo.  $4-5° 

"  It  is  well  worthy  the  careful  study  of  both  student  and  practitioner, 
and  can  not  fail  to  prove  of  great  value  to  both.  We  do  not  hesitate 
to  recommend  it." — Boston  Medical  and  Surgical  Journal. 

DIAGNOSIS. 

BROWN.  Medical  Diagnosis.  A  Manual  of  Clinical  Methods. 
4th  Edition.  112  Illustrations.  Cloth,  $2.25 

DA  COSTA.  Clinical  Hematology.  A  Practical  Guide  to  Exam- 
ination of  Blood.  6  Colored  Plates.  48  other  Illustrations.  Just 
Ready.  Cloth,  $5.00;  Sheep,  $6.00 

EMERY.  Bacteriological  Diagnosis.  2  Colored  Plates  and  32 
other  Illustrations.  I* -5° 

MEMMINGER.   Diagnosis  by  the  Urine.   sdEd.   24  Illus.  JSi.co 


MEDICAL  BOOKS.  11 


PERSHING.  Diagnosis  of  Nervous  and  Mental  Diseases. 
Illustrated.  $1.25 

STEELL.    Physical  Signs  of  Pulmonary  Disease.  $1.25 

TYSON.  Hand-Book  of  Physical  Diagnosis.  For  Students  and 
Physicians.  By  the  Professor  of  Clinical  Medicine  in  the  University 
of  Pennsylvania.  Illus.  4th  Ed.,  Improved  and  Enlarged.  With 
Two  Colored  and  55  other  Illustrations.  $1*50 


DENTISTRY. 

Special  Catalogue  of  Dental  Books  sent  free  upon  application. 

BARRETT.  Dental  Surgery  for  General  Practitioners  and 
Students  of  Medicine  and  Dentistry.  Extraction  of  Teeth, 
etc.  3d  Edition.  Illustrated.  $1.00 

BROOMELL.  Anatomy  and  Histology  of  the  Human  Mouth 
and  Teeth.  Second  Edition,  Revised  and  Enlarged.  337  Hand- 
some Illustrations.  Cloth,  14.50;  Leather,  $5. 50 

FILLEBROWN.  A  Text-Book  of  Operative  Dentistry. 
Written  by  invitation  ot  the  National  Association  of  Dental  Facul- 
ties. Illustrated.  $2.25 

QORGAS.  Dental  Medicine.  A  Manual  of  Materia  Medica  and 
Therapeutics,  yth  Edition.  Cloth,  $4.00 ;  Sheep,  $5.00 

GORGAS.  Questions  and  Answers  for  the  Dental  Student. 
Embracing  all  the  subjects  in  the  Curriculum  of  the  Dental  Student. 
Octavo.  |6.oo 

HARRIS.  Principles  and  Practice  of  Dentistry.  Including 
Anatomy,  Physiology,  Pathology,  Therapeutics,  Dental  Surgery, 
and  Mechanism.  131*1  Edition.  Revised  by  F.  J.  S.  GORGAS,  M.D., 
D.D.S.  1250  Illustrations.  Cloth,  £6.00;  Leather,  $7.00 

HARRIS.  Dictionary  of  Dentistry.  Including  Definitions  of  Such 
Words  and  Phrases  of  the  Collateral  Sciences  as  Pertain  to  the  Art  and 
Practice  of  Dentistry.  6th  Edition.  Revised  and  Enlarged  by  FER- 
DINAND F.  S.  GORGAS,  M.D.,  D.D.S.  Cloth,  $5.00 ;  Leather,  $6.00 

RICHARDSON.  Mechanical  Dentistry.  7th  Edition.  Thor- 
oughly Revised  and  Enlarged  by  DR.  GEO.  W.  WARREN.  691  Illus- 
trations. Cloth,  $5.00;  Leather,  $6.00 

SMITH.    Dental  Metallurgy,    zd  Edition.    Illustrated.  $2  oo 

TAFT.    Index  of  Dental  Periodical  Literature.  $2.00 

TOMES.    Dental  Anatomy.    Human  and  Comparative.    263  Illus- 
trations.   $th  Edition.  $4.00 
TOMES.     Dental  Surgery.    4th  Edition.    289  Illustrations.     $4.00 

WARREN.  Compend  of  Dental  Pathology  and  Dental  Medi- 
cine. With  a  Chapter  on  Emergencies.  3d  Edition.  Illustrated. 

.80;  Interleaved,  $1.25 

WARREN.  Dental  Prosthesis  and  Metallurgy.  129  Ills.  $1.25 
WHITE.    The  Mouth  and  Teeth.    Illustrated.  .40 


12  SUBJECT  CATALOGUE. 

DICTIONARIES  AND  CYCLOPEDIAS 

GOULD.    The  Illustrated  Dictionary  ot  Medicine,  Biology 

and  Allied  Sciences.     Being  an  Exhaustive  Lexicon  of  Medicine 

and  those  Sciences  Collateral  to  it:    Biology  (Zoology  and  Botany), 

Chemistry,  Dentistry,  Parmacology,  Microscopy,  etc.,  with  many 

useful  Tables  and  numerous  fine  Illustrations.     1633  pages,     sth  Ed. 

Sheep  or  Half  Morocco,  $10.00  ;  with  Thumb  Index,  jf n.oo 

Half  Russia,  Thumb  Index,  $12.00 

GOULD.  The  Medical  Student's  Dictionary,  nth  Edition. 
Illustrated.  Including  all  the  Words  and  Phrases  Generally  Used 
inMedicine,  with  their  Proper  Pronunciation  and  Definition,  Based 
on  Recent  Medical  Literature.  With  Table  of  Eponymic  Terms  and 
Tests  and  Tables  of  the  Bacilli,  Micrococci,  Mineral  Springs,  etc., 
of  the  Arteries,  Muscles,  Nerves,  Ganglia,  Plexuses,  etc.  nth  Edi- 
tion. Enlarged  and  illustrated  with  a  large  number  of  Engravings. 
840  pages.  Half  Morocco,  $2.50 ;  with  Thumb  Index,  £3.00 

GOULD.  The  Pocket  Pronouncing  Medical  Lexicon.  4th  Edi- 
tion. (30,000  Medical  Words  Pronounced  and  Defined.)  Containing 
all  the  Words,  their  Definition  and  Pronunciation,  that  the  Medical, 
Dental,  or  Pharmaceutical  Student  Generally  Comes  in  Contact 
With ;  also  Elaborate  Tables  of  Eponymic  Terms.  Arteries,  Muscles, 
Nerves,  Bacilli,  etc.,  etc.,  a  Dose  List  in  both  English  and  Metric 
Systems,  etc.,  Arranged  in  a  Most  Convenient  Form  for  Reference  and 
Memorizing.  Fourth  Edition,  Revised  and  Enlarged.  838 
pages.  Full  Limp  Leather,  Gilt  Edges,  $1.00  ;  Thumb  Index,  $1.25 
145,000  Copies  of  Gould's  Dictionaries  Have  Been  Sold. 

GOULD  AND  PYLE.  Cyclopedia  of  Practical  Medicine  and 
Surgery.  Seventy-two  Special  Contributors.  Illustrated. 
One  Volume.  A  Concise  Reference  Handbook  of  Medicine, 
Surgery,  Obstetrics,  Materia  Medica,  Therapeutics,  and  the  Various 
Specialties,  with  Particular  Reference  to  Diagnosis  and  Treatment. 
Compiled  under  the  Editorial  Supervision  of  GEORGE  M.  GOULD, 
M.D.,  Author  of  "  An  Illustrated  Dictionary  of  Medicine,"  etc.; 
and  WALTER  L.  PYLE,  M.D.,  Assistant  Surgeon  Wills  Eye 
Hospital ;  formerly  Editor  "  International  Medical  Magazine,"  etc., 
and  Seventy-two  Special  Contributors.  With  many  Illustrations. 
Large  Square  8vo,  to  correspond  with  Gould's  "  Illustrated  Dic- 
tionary." Full  Sheep  or  Half  M  or.,  $10.00;  with  Thumb  Index,  $11.00 
Half  Russia,  Thumb  Index,  $12.00  net. 

GOULD  AND  PYLE.  Pocket  Cyclopedia  of  Medicine  and 
Surgery.  Based  upon  above  book  and  uniform  in  size  with  "  Gould's 
Pocket  Dictionary." 

Full  Limp  Leather,  Gilt  Edges,  $1.00,  with  Thumb  Index,  $1.25 

HARRIS.  Dictionary  of  Dentistry.  Including  Definitions  of  Such 
Words  and  Phrases  of  the  Collateral  Sciences  as  Pertain  to  the  Art 
and  Practice  of  Dentistry.  6th  Edition.  Revised  and  Enlarged  by 
FERDINAND  J.  S.  GORGAS,  M.D.,  D.D.S.  Cloth,  $5.00;  Leather,  $6.00 

LONGLEY.     Pocket  Medical  Dictionary.  Cloth,  .75 

MAXWELL.  Terminologia  Medica  Polyglotta.  By  Dr. 
THEODORE  MAXWELL,  Assisted  by  Others.  $3.00 

The  object  of  this  work  is  to  assist  the  medical  men  ot  any  nationality 

in  reading  medical  literature  written  in  a  language  not  their  own. 

Each  term  is  usually  given  in  seven  languages,  viz. :  English,  French, 

German,  Italian,  Spanish,  Russian,  and  Latin. 

TREVES  AND  LANG.    German-English  Medical  Dictionary . 

Half  Calf,  $3.25 


MEDICAL  BOOKS.  13 


EAR  (see  also  Throat  and  Nose). 

BURNETT.    Hearing  and  How  to  Keep  It.    Illustrated.         .40 
HOVELL.    Diseases  oi  the  Ear  and  Naso-Pharynx.    Includ- 
ing Anatomy  and  Physiology  of  the  Organ,  together  with  the  Treat- 
ment of  the  Affections  of  the  Nose  and  Pharynx  which  Conduce  to 
Aural  Disease.     128  Illustrations.     2d  Edition.  $.S>5o 

PRITCHARD.     Diseases  of  the  Ear.     4th  Edition,  Enlarged. 
Many  Illustrations  and  Formula.  In  Press. 


ELECTRICITY. 

BIGELOW.  Plain  Talks  on  Medical  Electricity  and  Bat- 
teries. With  a  Therapeutic  Index  and  a  Glossary.  43  Illustra- 
tions, ad  Edition.  £1.00 

HEDLEY.  Therapeutic  Electricity  and  Practical  Muscle 
Testing.  QQ  Illustrations.  $2.50 

JACOBY.      Electrotherapy.     2    Vols.    Illustrated.      See    Cohen, 

Physiologic  Therapeutics,  page  id. 
JONES.   Medical  Electricity.  3.1  Edition.   117  Illus.  $3.00 


EYE. 

A  Special  Circular  of  Books  on  the  Eye  sent  frte  upon  application. 

DONDERS.  The  Nature  and  Consequences  of  Anomalies  of 
Refraction.  With  Portrait  and  Illustrations.  Half  Morocco,  fi. 25 

PICK.  Diseases  of  the  Eye  and  Ophthalmoscopy.  Trans- 
lated by  A.  B.  HALE,  M.  D.  157  Illustrations,  many  of  which  are  in 
colors,  and  a  glossary.  Cloth,  $4.50 ;  Sheep,  15.50 

GOULD  AND  PYLE.  Compend  of  Diseases  of  the  Eye  and 
Refraction.  Including  Treatment  and  Operations,  and  a  Section 
on  Local  Therapeutics.  With  Formulae,  Useful  Tables,  a  Glossary, 
and  in  Illus.,  several  of  which  are  in  colors.  2d  Edition,  Revised. 

Cloth,  .80;  Interleaved,  £1.00 

GREEFF.  The  Microscopic  Examination  of  the  Eye.  Illus- 
trated. $1.25 

HARLAN.    Eyesight,  and  How  to  Care  for  It.    Illus.  .40 

HARTRIDGE.  Refraction.  104  Illustrations  and  Test  Types, 
nth  Edition,  Enlarged.  $1.50 

HARTRIDGE.  On  the  Ophthalmoscope.  4th  Edition.  With 
4  Colored  Plates  and  68  Wood-cuts.  $1.50 

HANSELL  AND  REBER.  Muscular  Anomalies  of  the  Eye. 
Illustrated.  £1.50 

HANSELL  AND  BELL.  Clinical  Ophthalmology.  Colored 
Plate  of  Normal  Fundus  and  120  Illustrations.  $1.50 

JENNINGS.  Manual  of  Ophthalmoscopy.  95  Illustrations  and 
i  Colored  Plate.  £1.50 


14  SUBJECT  CATALOGUE. 

MORTON.  Refraction  of  the  Eye.  Its  Diagnosis  and  the  Cor- 
rection of  its  Errors.  6th  Edition.  $1.00 

OHLEMANN.  Ocular  Therapeutics.  Authorized  Translation, 
and  Edited  by  DR.  CHARLES  A.  OLIVER.  $1.75 

PARSONS.  Elementary  Ophthalmic  Optics.  With  Diagram- 
matic Illustrations.  $2.00 

PHILLIPS.  Spectacles  and  Eyeglasses.  Their  Prescription 
and  Adjustment  3d  Edition.  52  Illustrations.  Just  Ready.  $1.00 

SWANZY.  Diseases  of  the  Eye  and  Their  Treatment.  7th 
Edition,  Revised  and  Enlarged.  164  Illustrations,  i  Plain  Plate, 
and  a  Zephyr  Test  Card .  $2 . 50 

From  The  Medical  News. 

"  Swanzy  has  succeeded  in  producing  the  most  intellectually  con- 
ceived and  thoroughly  executed  resume  of  the  science  within  the 
limits  he  has  assigned  himself.  As  a  '  students'  handbook,'  small 
in  size  and  of  moderate  price,  it  can  hardly  be  equaled." 

THORINGTON.  Retinoscopy.  4th  Edition,  Carefully  Revised. 
Illustrated.  Ji.oo 

THORINGTON.  Refraction  and  How  to  Refract.  200  Illustra- 
tions, 13  of  which  are  Colored.  2d  Edition.  $1.50 

WALKER.  Students'  Aid  in  Ophthalmology.  Colored  Plate 
and  40  other  Illustrations  and  Glossary.  $1.50 

WRIGHT.  Ophthalmology,  ad  Edition,  Revised  and  Enlarged. 
117  Illustrations  and  a  Glossary.  $3.00 


FEVERS. 

HBOURN.    Fi 

HEART. 

Methods  of  th 
i  Edition.    Illustr 

HISTOLOGY. 


GOODALL  AND  WASHBOURN.    Fevers  and  Their  Treat- 
ment.   Illustrated.  $3.00 


THORNE.    The  Schott  Methods  of  the  Treatment  of  Chronic 
Heart  Disease.    Fourth  Edition.    Illustrated.  $2.00 


GUSHING.  Compend  of  Histology.  By  H.  H.  GUSHING,  M.D., 
Demonstrator  of  Histology,  Jefferson  Medical  College,  Philadelphia. 
Illustrated.  Nearly  Ready.  .80;  Interleaved,  $1.00 

LAZARUS-BARLOW.  Pathological  Anatomy  and  His- 
tology. Illustrated.  $6.50 

STIRLING.  Outlines  of  Practical  Histology.  368  Illustrations, 
ad  Edition,  Revised  and  Enlarged.  With  new  Illustrations.  $2.00 

STOHR.  Histology  and  Microscopical  Anatomy.  Edited  by 
A.  SCHAPBR,  M.D.,  University  of  Breslau,  formerly  Demonstrator  of 
Histology,  Harvard  Medical  School.  Fourth  American  from  gth  Ger- 
man Edition,  Revised  and  Enlarged.  379  Illustrations.  $3.00 


MEDICAL  BOOKS.  15 


HYGIENE  AND  WATER  ANALYSIS. 

Sficial  Catalog**  of  Books  on  Hygiene  sent  free  upon  application. 

CANPIELD.  Hygiene  of  the  Sick-Room.  A  Book  for  Nurses 
and  Others.  Being  a  Brief  Consideration  of  Asepsis,  Antisepsis,  Dis- 
infection, Bacteriology,  Immunity,  Heating,  Ventilation,  etc.  $1.25 

CONN.    Agricultural  Bacteriology.    Illustrated.  $2.50 

COPLIN.  Practical  Hygiene.  A  Complete  American  Text-Book. 
138  Illustrations.  New  Edition.  Preparing. 

HARTSHORNE.    Our  Homes.     Illustrated.  .40 

KENWOOD.  Public  Health  Laboratory  Work.  116  Illustra- 
tions and  3  Plates.  $2.00 

LEFFMANN.  Select  Methods  in  Food  Analysis.  53  Illustra- 
tions and  4  Plates.  $2.50 

LEFFMANN.  Examination  ot  Water  for  Sanitary  and 
Technical  Purposes.  4th  Edition.  Illustrated.  $1.25 

LEFFMANN.  Analysis  of  Milk  and  Milk  Products.  Illus- 
trated. Second  Edition.  $1.25 

LINCOLN.    School  and  Industrial  Hygiene.  .40 

McFARLAND.  Prophylaxis  and  Personal  Hygiene.  Care  of 
the  Sick.  See  Cohen,  Physiologic  Therapeutics , page  ib. 

NOTTER.  The  Theory  and  Practice  of  Hygiene.  15  Plates 
and  138  other  Illustrations.  8vo.  2d  Edition.  £7.00 

PARKES  AND  KENWOOD.  Hygiene  and  Public  Health. 
2d  Edition,  Enlarged.  Illustrated.  $3.00 

ROSENAU.    Disinfection  and  Disinfectants.    Illustrated.  $2.00 

STARR.  The  Hygiene  of  the  Nursery.    Including  the  General 

Regimen  and  Feeding  of  Infants  and  Children,  and  the  Domestic 

Management  of  the  Ordinary  Emergencies  of  Early  Life,  Massage, 

etc.    6th  Edition.    25  Illustrations.  £1.00 

STEVENSON  AND  MURPHY.    A  Treatise  on  Hygiene.    By 

Various  Authors.     In    Three    Octave   Volumes.    Illustrated. 

Vol.  I,  $6.00;  Vol.  II,  $6.00;  Vol.  Ill,  £5-00 

%*  Each  Volume  sold  separately.  Special  Circular  upon  application. 
THRESH.    Water  and  Water  Supplies,    sd  Edition.          £2.00 

WILSON.  Hand-Book  of  Hygiene  and  Sanitary  Science. 
Wiih  Illustrations.  8th  Edition.  $3.00 

WEYL.  Sanitary  Relations  of  the  Coal-Tar  Colors.  Author- 
ized Translation  by  HENRY  LEFFMANN,  M.D.,  PH.D.  $1.25 


LUNGS  AND  PLEURA. 

KNOPF.     Pulmonary  Tuberculosis.     Its  Modern  Prophylaxis 
and  Treatment  in  Special  Institutions  and  at  Home,     lllus.        #3.00 

STEELL.    Physical  Signs  of  Pulmonary  Disease.  lllus.  $1.25 


16  SUBJECT  CATALOGUE. 

MASSAGE—  PHYSICAL  EXERCISE. 

OSTROM.  Massage  and  the  Original  Swedish  Move- 
ments. Their  Application  to  Various  Diseases  of  the  Body.  A 
Manual  for  Students,  Nurses,  and  Physicians.  Fifth  Edition,  En- 
larged. 115  Illustrations,  many  of  which  are  original.  |i.oo 

MITCHELL  AND  GULICK.  Mechanotherapy,  Physical 
Education,  etc.  Illustrated.  See  Cohen,  Physiologic  Therapeu- 
tics, below. 

TREVES.     Physical  Education.    Its  Value,  Methods,  etc.         .75 

MATERIA    MEDICA    AND    THERA- 
PEUTICS. 

BRACKEN.    Outlines  of  Materia  Medica  and  Pharmacology.    $2.75 

COBLENTZ.  The  Newer  Remedies.  Including  their  Synonyms, 
Sources,  Methods  of  Preparation,  Tests,  Solubilities,  Doses,  etc. 
3d  Edition,  Enlarged  and  Revised.  $1.00 

COHEN.  Physiologic  Therapeutics.  Methods  other  than  Drug- 
Giving  useful  in  the  Prevention  of  Disease  and  in  the  Treatment  of 
the  Sick.  Mechanotherapy,  Mental  Therapeutics,  Suggestion, 
Electrotherapy,  Climatology,  Hydrotherapy,  Pneumatotherapy, 
Prophylaxis,  Dietetics,  Organotherapy,  Phototherapy,  Mineral 
Waters,  Baths,  etc.  n  Volumes,  Octavo.  Illustrated.  (Subscrip- 
tion.) Cloth,  $27.50  ;  }£  mor.,  $38.50 

Special  Descriptive  Circular  -will  be  sent  upon  application. 

DAVIS.    Materia  Medica  and  Prescription  Writing.       £1.50 

OORQAS.  Dental  Medicine.  A  Manual  of  Materia  Medica  and 
Therapeutics,  yth  Edition,  Revised.  $4.00 

GROFF.  Materia  Medica  for  Nurses,  with  questions  for  Self-  Exam- 
ination. ad  Edition,  Revised  and  Improved.  fust  Ready.  $1.25 

HELLER.  Essentials  of  Materia  Medica,  Pharmacy,  and 
Prescription  Writing.  $1-50 

MAYS.    Theine  in  the  Treatment  of  Neuralgia.    %  bound,  .50 

POTTER.    Hand-Bopk  of  Materia  Medica,  Pharmacy,  and 

Therapeutics,  including  the  Action  of  Medicines,  Special  Therapeu- 

tics, Pharmacology,  etc.,  including  over  600  Prescriptions  and  For- 

mulae.   9th  Edition,  Revised  and  Enlarged.     With  Thumb  Index  in 

each  copy.    Just  Ready.  Cloth,  $5.00;  Sheep,  $6.00 

"  In  conclusion  we  may  add  that  Dr.  Potter's  Therapeutics  covers  a 

Vider  field  than  many  books  which  bear  this  title.     He  discusses  a 

good  many  drugs  which  are  rarely  employed,  and  therefore  the  book 

is  as  useful  to  one  who  wishes  to  look  for  unusual  information  as  it  is  to 

him  who  wishes  a  handbook  for  ready  jeference  in  the  treatment  of 

disease  as  he  meets  it  from  day  to  day.  —  Therapeutic  Gazette. 

POTTER. 
Prescrip 
cal  Actio 

MURRAY.    Rough  Notes  on  Remedies.    4th  Edition.         $1.25 


OTTER.  Compend  of  Materia  Medica,  Therapeutics,  and 
Prescription  Writing,  with  Special  Reference  to  the  Physiologi- 
cal Action  of  Drugs.  6th  Edition.  .80;  Interleaved,  $1.00 


MEDICAL  BOOKS.  17 


SAYRE.  Organic  Materia  Medica  and  Pharmacognosy.  An 
Introduction  to  the  Study  of  the  Vegetable  Kingdom  and  the  Vege- 
table and  Animal  Drugs.  Comprising  the  Botanical  and  Physical 
Characteristics,  Source,  Constituents,  and  Pharmacopeial  Prepara- 
tions, Insects  Injurious  to  Drugs,  and  Pharmacal  Botany.  With 
sections  on  Histology  and  Microtechnique,  by  W.  C.  STEVENS. 
374  Illustrations,  many  of  which  are  original.  2d  Edition. 

Cloth,  $4-50 

TAVERA.    Medicinal  Plants  of  the  Philippines.  $2.00 

WHITE  AND  WILCOX.  Materia  Medica,  Pharmacy,  Phar- 
macology, and  Therapeutics,  sth  American  Edition,  Revised  by 
REYNOLD  W.  WILCOX,  M.A.,  M.D.,  LL.D.,  Professor  of  Clinical 
Medicine  and  Therapeutics  at  the  New  York  Post-Graduate  Medical 
School.  Cloth,  $3.00 ;  Leather,  $3.50 

"  The  care  with  which  Dr.  Wilcox  has  performed  his  work  is  con- 
spicuous on  every  page,  and  it  is  evident  that  no  recent  drug  possess- 
ing any  merit  has  escaped  his  eye.  We  believe,  on  the  whole,  this  is 
the  best  book  on  Materia  Medica  and  Therapeutics  to  place  in  the 
hands  of  students,  and  the  practitioner  will  find  it  a  most  satisfactory 
work  for  daily  use."—  The  Cleveland  Medical  Gazette. 

MEDICAL    JURISPRUDENCE     AND 
TOXICOLOGY. 

REESE.  Medical  Jurisprudence  and  Toxicology.  A  Text-Book 
for  Medical  and  Legal  Practitioners  and  Students.  6th  Edition. 
Revised  by  HENRY  LBFFMANN,  M.D.  Clo.,  $3.00;  Leather,  $3.50 

"  To  the  student  of  medical  jurisprudence  and  toxicology  it  is  in- 
valuable, as  it  is  concise,  clear,  and  thorough  in  every  respect." — The 
American  Journal  of  the  Medical  Sciences. 

MANN.    Forensic  Medicine  and  Toxicology.    Illus.          $6.50 

TANNER.  Memoranda  of  Poisons.  Their  Antidotes  and  Tests. 
9th  Edition,  by  DR.  HENRY  LEFFMANN.  Just  Ready.  .75 

MICROSCOPY. 

CARPENTER.     The  Microscope  and    Its   Revelations.    Sth 

Edition,  Revised  and  Enlarged.      817  Illustrations  and  23   Plates. 
Cloth,  $8.00  ;  Half  Morocco,  $9.00 

LEE.  The  Microtomist's  Vade  Mecum.  A  Hand-Book  of 
Methods  of  Microscopical  Anatomy.  887  Articles.  5th  Edition, 
Enlarged.  |4-<x 

OERTEL.  Medical  Microscopy.  A  Guide  to  Diagnosis,  Ele- 
mentary Laboratory  Methods  and  Microscopic  Technic.  131  Illus- 
trations. Just  Ready.  $2.00 

REEVES.  Medical  Microscopy,  including  Chapters  on  Bacteri- 
ology, Neoplasms,  Urinary  Examination,  etc.  Numerous  Illus- 
trations, some  of  which  are  printed  in  colors.  $2.50 

WETHERED.  Medical  Microscopy.  A  Guide  to  the  Use  of  the 
Microscope  in  Practical  Medicine.  100  Illustrations.  $2.00 


18  SUBJECT  CATALOGUE. 

MISCELLANEOUS. 

BERRY.    Diseases  of  Thyroid  Gland.    Illustrated.  $4.00 

BURNETT.     Poods  and  Dietaries.    A  Manual  of  Clinical  Diet- 
etics.   2d  Edition.  $1-50 
BUXTON.    Anesthetics.    Illustrated.    3d  Edition.                  $1.50 

COHEN.  Organotherapy.  See  Cohen,  Physiologic  Therapeutics, 
Page  ib. 

DAVIS.  Dietotherapy.  Food  in  Health  and  Disease.  With 
Tables  of  Dietaries,  Relative  Value  of  Foods,  etc.  See  Cohen, 
Physiologic  Therapeutics,  page  ib. 

FRENKEL.     Tabetic  Alaxia.     Illus.    Just  Ready.  $3.00 

GOULD.  Borderland  Studies.  Miscellaneous  Addresses  and 
Essays,  remo.  $2.00 

GOULD.  Biographic  Clinics.  The  Origin  of  the  Ill-Health  ot 
DeQaincy,CarIyle,  Darwin,  Huxley  and  Browning.  JustReady.  $i.co 

GREENE.  Medical  Examination  for  Life  Insurance.  Illus- 
trated. With  Colored  and  other  Engravings.  2d  Ed.  In  Press. 

HAIG.  Causation  of  Disease  by  Uric  Acid.  The  Pathology  of 
High  Arterial  Tension,  Headache,  Epilepsy,  Gout,  Rheumatism, 
Diabetes,  Bright's  Disease,  etc.  sthEdition.  $3-°o 

HAIG.  Diet  and  Food.  Considered  in  Relation  to  Strength  and 
Power  of  Endurance.  4th  Edition.  Ji.oo 

HENRY.    A  Practical  Treatise  on  Anemia.         Half  Cloth,  .50 

LEFFMANN.     Food  Analysis.    Illustrated.  $2.50 

NEW  SYDENHAM  SOCIETY'S  PUBLICATIONS.  Circulars 
upon  application.  Per  Annum,  $8.00 

OSGOOD.    The  Winter  and  Its  Dangers.  .40 

PACKARD.     Sea  Air  and  Sea  Bathing.  .40 

RICHARDSON.    Long  Life  and  How  to  Reach  It.  .40 

TISSIER.  Pneumatotherapy.  See  Cohen,  Physiologic  Therapeu- 
tics, page  ib. 

TURNBULL.    Artificial  Anesthesia.     4th  Edition.    Illus.   $2.50 

WEBER    AND     HINSDALE.       Climatology    and     Health 

Resorts.     Including   Mineral  Springs.     2  Vols.     Illustrated  with 

Colored  Maps.     See  Cohen,  Physiologic  Therapeutics,  page  ib. 

WILSON.    The  Summer  and  Its  Diseases.  .40 

WINTERNITZ.  Hydrotherapy,  Thermotherapy,  Photo- 
therapy, Mineral  Waters,  Baths,  etc.  Illustrated.  See  Cohen, 
Physiologic  Therapeutics,  page  ib. 

NERVOUS  DISEASES. 

DERCUM.  Rest,  Suggestion,  Mental  Therapeutics.  See 
Cohen,  Physiologic  Therapeutics, page  ib. 

GORDINIER.  The  Gross  and  Minute  Anatomy  of  the  Cen- 
tral Nervous  System.  With  271  original  Colored  and  other 
Illustrations.  Cloth,  $6.00;  Sheep,  $7.00 

GOWERS.    Syphilis  and  the  Nervous  System. 


MEDICAL  BOOKS.  19 


QOWERS.    Manual  of  Diseases  of  the  Nervous  System.    A 
Complete  Text-Book.     Revised,  Enlarged,  and  in  many  parts  Re- 
written.    With  many  new  Illustrations.    Two  volumes. 
Vol.  I.   Diseases  of  the  Nerves  and  Spinal  Cord,    ad  Edition,  En- 
larged. Cloth,  $4.00 ;  Sheep,  $5.00 
Vol.  II.    Diseases  of    the  Brain  and  Cranial  Nerves ;   General  and 
Functional  Disease,    ad  Edition.              Cloth,  £4.00;  Sheep,  £5.00 

QOWERS.   Epilepsy  and  Otker  Chronic  Convulsive  Diseases. 

3d  Edition.  $3-°° 

HORSLEY.    The  Brain  and  Spinal  Cord.    The  Structure  and 

Functions  of.     Numerous  Illustrations.  $2-5° 

ORMEROD.    Diseases  of  the  Nervous  System.    66  Wood  En. 
gravings.  .         $1.00 

PERSHING.     Diagnosis  of  Nervous  and  Mental  Diseases. 

Illustrated.  $1.25 

PRESTON.  Hysteria  and  Certain  Allied  Conditions.  Their 

Nature  and  Treatment.  Illustrated.  $2.00 

WOOD.  Brain  Work  and  Overwork.  .40 


NURSING  (see  also  Massage). 

Special  Catalogue  of  Books  for  Nurses  sent  free  upon  application. 

CANFIELD.  Hygiene  of  the  Sick-Room.  A  Book  for  Nurses  and 
Others.  Being  a  Brief  Consideration  of  Asepsis,  Antisepsis,  Disinfec- 
tion, Bacteriology,  Immunity,  Heating  and  Ventilation,  and  Kindred 
Subjects  for  the  Use  of  Nurses  and  Other  Intelligent  Women.  $1.25 

CUFF.    Lectures  to  Nurses  on  Medicine.    Third  Edition.    $1.25 

DAVIS.  Bandaging.  Its  Principles  and  Practice.  163  Original 
Illustrations.  Just  Ready.  $1-50 

DOMVILLE.  Manual  for  Nurses  and  Others  Engaged  in  At- 
tending the  Sick,  gth  Edition.  With  Recipes  for  Sick-room  Cook- 
ery, etc.  In  Press. 

FULLERTON.    Obstetric  Nursing.    41  Ills,    sth  Ed.          Ji.oo 

FULLERTON.     Surgical    Nursing,    sd  Ed.    69  Ills.          Ji.oo 

QROFF.  Materia  Medica  for  Nurses.  With  Questions  for  Self-Ex- 
amination. 2d  Edition,  Revised  and  Improved.  Just  Ready.  $1.25 

HADLEY.  General,  Medical,  and  Surgical  Nursing.  A  very 
Complete  Manual,  Including  Sick-Room  Cookery.  fa-^S 

HUMPHREY.  A  Manual  for  Nurses.  Including  General 
Anatomy  and  Physiology,  Management  of  the  Sick  Room,  etc. 
23d  Edition.  79  Illustrations.  fi.oo 

STARR.  The  Hygiene  of  the  Nursery.  Including  the  General 
Regimen  and  Feeding  of  Infants  and  Children,  and  the  Domestic  Man- 
agement of  the  Ordinary  Emergencies  of  Early  Life,  Massage,  etc.  6th 
Edition.  25  Illustrations.  £1.00 

TEMPERATURE  AND  CLINICAL  CHARTS.    See  page  24. 

VOSWINKEL.  Surgical  Nursing.  Second  Edition,  Enlarged, 
us  Illustrations.  Ji.oo 


20  SUBJECT  CATALOGUE. 

OBSTETRICS. 

CAZEAUX  AND  TARNIER.  Midwifery.  With  Appendix  by 
MuNDft.  The  Theory  and  Practice  of  Obstetrics,  including  the  Dis- 
eases ot  Pregnancy  and  Parturition,  Obstetrical  Operations,  etc. 
8th  'Edition.  Illustrated  by  Colored  and  other  full-page  Plates,  and 
numerous  Wood  Engravings.  Cloth,  $4.50 ;  Full  Leather,  $5.50 

EDGAR.  Text-Book  of  Obstetrics.  By  J.  CLIFTON  EDGAR, 
M.D.,  Professor  of  Obstetrics,  Medical  Department  of  Cornell 
University,  New  York  City.  Elaborately  Illustrated.  In  Press. 

FULLERTON.    Obstetric  Nursing,     sth  Ed.    Illustrated.    $1.00 

LANDIS.  Compend  of  Obstetrics.  7th  Edition,  Revised  by  WM. 
H.  WELLS,  Demonstrator  of  Clinical  Obstetrics,  Jefferson  Medical 
College:  52  Illustrations.  .80  ;  Interleaved,  $1 .00 

WINCKEL.  Text-Book  of  Obstetrics,  Including  the  Pathol- 
ogy and  Therapeutics  of  the  Puerperal  State.  Iiius.  $5.00 

PATHOLOGY— BACTERIOLOGY. 

BLACK.     Micro-Organisms.     The  Formation  of  Poisons.  .75 

BLACKBURN.  Autopsies.  A  Manual  of  Autopsies  Designed  for 
the  Use  ot  Hospitals  for  the  Insane  and  other  Public  Institutions. 
Ten  full-page  Plates  and  other  Illustrations.  $1-25 

CONN.    Agricultural  Bacteriology.    Illustrated.  $2.50 

CONN.    Bacteria  in  Milk  and  Its  Products.    Illustrated.  $1.25 
COPLIN.  Manual  of  Pathology.  Including  Bacteriology,  Technic 
of  Post-Mortems,  Methods  of  Pathologic  Research,  etc.     330  Illus- 
trations, 7  Colored  Plates.     3d  Edition.  $3-5° 
DA  COSTA.     Clinical  Hematology.     A  Practical  Guide  to  the 
Examination  of  the  Blood.    Six  Colored  Plates  and  48  Illustrations. 

Cloth,  $5.00 ;  Sheep,  $6.00 

EMERY.    Bacteriological  Diagnosis.    2  Colored  Plates  and  32 

other  Illustrations.  $i-5° 

HEWLETT.    Manual  of  Bacteriology.   75  Illustrations.    Second 

Edition,  Revised  and  Enlarged.    Just  Ready.  $4.00 

LAZARUS-BARLOW.     Pathological  Anatomy.  $6.50 

ROBERTS.  Gynecological  Pathology.   Illustrated.  $6.00 

SMITH.    Laboratory  Exercises  in  Bacteriology.    Illustrated. 

Just  Ready.  $1.5° 

THAYER.       Compend    of    General    Pathology.       Illustrated. 

.80;  Interleaved,  %\. oo 
THAYER.     Compend  of  Special  Pathology.     Illustrated. 

.80 ;  Interleaved,  $1.00 

VIRCHOW.     Post-Mortem  Examinations.    3d  Edition.         .75 
WHITACRE.     Laboratory  Te-xt-Book  of   Pathology.     With 
121  Illustrations.  $i-5° 

WILLIAMS.  Bacteriology.  A  Manual  for  Students.  90  Illus- 
trations, ad  Edition,  Revised.  $1.5° 

PHARMACY. 

Special  Catalogue  ot  Books  on  Pharmacy  sent  free  upon  application. 

COBLENTZ.  Manual  of  Pharmacy.  A  Complete  Text-Book 
by  the  Professor  in  the  New  York  College  of  Pharmacy,  ad  Edition, 
Revised  and  Enlarged.  437  Illus.  Cloth,  $3.50;  Sheep,  $4.50 

COBLENTZ.    Volumetric  Analysis.    Illustrated.  $1.25 


MEDICAL  BOOKS.  21 


BEASLEY.  Book  of  3100  Prescriptions.  Collected  from  the 
Practice  of  the  Most  Eminent  Physicians  and  Surgeons — English, 
French,  and  American.  A  Compendious  History  ot  the  Materia 
Medica,  Lists  of  the  Doses  of  all  the  Officinal  and  Established  Pre- 
parations, an  Ipdex  of  Diseases  and  their  Remedies,  yth  Ed.  $2.00 

BEASLEY.  Druggists'  General  Receipt  Book.  Comprising 
a  Copious  Veterinary  Formulary,  Recipes  in  Patent  and  Proprietary 
Medicines,  Druggists'  Nostrums,  etc. ;  Perfumery  and  Cosmetics, 
Beverages,  Dietetic  Articles  and  Condiments,  Trade  Chemicals, 
Scientific  Processes,  and  many  Useful  Tables.  loth  Ed.  $2.00 

BEASLEY.  Pharmaceutical  Formulary.  A  Synopsis  of  the 
British,  French,  German,  and  United  States  Pharmacopoeias.  Com- 
prising Standard  and  Approved  Formulae  for  the  Preparations  and 
Compounds  Employed  in  Medicine.  iath  Edition.  $2.00 

PROCTOR.  Practical  Pharmacy,  $d  Edition,  with  Illustrations 
and  Elaborate  Tables  of  Chemical  Solubilities,  etc.  $3.00 

ROBINSON.     Latin  Grammar  of  Pharmacy  and   Medicine. 

3d  Edition.     With  elaborate  Vocabularies.  $J-75 

SAYRE.  Organic  Materia  Medica  and  Pharmacognosy.  An 
Introduction  to  the  Study  of  the  Vegetable  Kinedom  and  the  Vege- 
table and  Animal  Drugs.  Comprising  the  Botanical  and  Physical 
Characteristics,  Source,  Constituents,  and  Pharmacopeial  Prepar- 
ations, Insects  Injurious  to  Drugs,  and  Parmacal  Botany.  With 
sections  on  Histology  and  Microtechnique,  by  W.  C.  STEVENS. 
374  Illustrations.  Second  Edition.  Cloth,  $4.50 

SCOVILLE.    The  Art  of  Compounding.    Second  Edition,  Re- 
vised and  Enlarged.  ,  Cloth,  $2.50 
STEWART.      Compend  of  Pharmacy.     Based  upon  "  Reming- 
ton's  Text-Book  of  Pharmacy."      sth  Edition,  Revised  in  Accord- 
ance with  the  U.  S.  Pharmacopoeia,  1890.      Complete   Tables  ot 
Metric  and  English  Weights  and  Measures.     .80;   Interleaved,  $1.00 
TAVERA.     Medicinal  Plants  of  the  Philippines.  $2.00 
UNITED  STATES  PHARMACOPOEIA.  7th  Decennial  Revision. 
Cloth,  $2.50  (postpaid,  #2.77)  ;  Sheep,  $3.00  (postpaid,  $3.27) ;  Inter- 
leaved, $4.00  (postpaid,  $4.50);  Printed  on  one  side  of  page  only, 
unbound,  $3.50  (postpaid,  $3.90). 

Select  Tables  from  the  U.  S.  P.    Being  Nine  of  the  Most  Impor- 
tant and  Useful  Tables,  Printed  on  Separate  Sheets.  .25 
POTTER.      Hand-Book  of  Materia  Medica,  Pharmacy,  and 
Therapeutics.    600  Prescriptions.    Sth  Ed.    Clo.,  $5.00;  Sh.,  $6.00 


PHYSIOLOGY. 

BIRCH.  Practical  Physiology.  An  Elementary  Class  Book. 
62  Illustrations.  $*-75 

BRUBAKER.  Compend  oi  Physiology,  nth  Edition,  Revised 
and  Enlarged.  Illustrated.  Just  Ready,  80;  Interleaved,  $i  .00 

JONES.    Outlines  of  Physiology.    96  Illustrations.  $1.50 

KIRKES.  Handbook  of  Physiology,  ijth  Authorized  Edition. 
Revised,  Rearranged,  and  Enlarged.  By  PROF.  W.  D.  HALLIBUR- 
TON, of  Kings  College,  London.  681  Illustrations,  some  of  which 
are  in  colors.  Cloth,  $3.00 ;  Leather  $3.75 


22  SUBJECT  CATALOGUE. 

LANDOIS.  A  Text-Book  of  Human  Physiology,  Including 
Histology  and  Microscopical  Anatomy,  with  Special  Reference  to 
the  Requirements  of  Practical  Medicine,  sth  American,  translated 
from  the  last  German  Edition,  with  Additions  by  WM.  STIRLING, 
M.D.,D.SC.  845  Illus.,  many  of  which  are  printed  in  colors.  In  Press. 

STARLING.     Elements  of  Human  Physiology.    loollls.    fi.oo 

STIRLING.  Outlines  of  Practical  Physiology.  Including 
Chemical  and  Experimental  Physiology,  with  Special  Reference  to 
Practical  Medicine.  3d  Edition.  289  Illustrations.  $2.00 

TYSON.    Cell  Doctrine.    Its  History  and  Present  State.        $1.50 

PRACTICE. 

BEALE.    On  Slight  Ailments ;  their  Nature  and  Treatment. 

2d  Edition,  Enlarged  and  Illustrated.  i?-25 

FAGGE.  Practice  of  Medicine.  4th  Edition,  by  P.  H.  PYK- 
SMITH.MD.  2  Volumes.  Vol.  I, $6.00  ;  Vol.  II, $6.00 

FOWLER.      Dictionary  of   Practical   Medicine.      By  various 
writers.  An  Encyclopaedia  of  Medicine.  Clo.,$3.oo;  Half  Mor.  $4.00 
GOULD  AND  PYLE.    Cyclopedia  of  Practical  Medicine  and 
Surgery.     A  Concise  Reference  Handbook,  with  particular  Refer- 
ence  to  Diagnosis  and   Treatment      Edited  by    DRS    GOULD    and 
PYLE,  Assisted  by  72  Special  Contributors.     Illustrated,  one  volume. 
Large  Square  Octavo,  Uniform  with  "Gould's  Illustrated  Diction- 
ary." Sheep  or  Half  Mor.,  $10.00 ;  with  Thumb  Index,  $11.00 
Half  Russia,  Thumb  Index,  $12  oo 

O~  Complete  descriptive  circular  free  upon  application. 
GOULD  AND  PYLE'S  Pocket  Cyclopedia  of  Medicine  and 
Surgery.     Based  upon  the   above   and    Uniform  with   "  Gould's 
Pocket  Dictionary."  Full  Limp  Leather,  Gilt  Edges,  Round  Corners, 
$1.00.     With  Thumb  Index,  $1.25 

HUGHES.  Compend  of  the  Practice  of  Medicine.  6th  Edition, 
Revised  and  Enlarged. 

Part  I.  Continued,  Eruptive,  and  Periodical  Fevers,  Diseases  of  the 
Stomach,  Intestines,  Peritoneum,  Biliary  Passages,  Liver,  Kid- 
neys, etc.,  and  General  Diseases,  etc. 

Part  II.  Diseases  of  the  Respiratory  System,  Circulatory  System, 
and  Nervous  System;  Diseases  of  the  Blood,  etc. 

Price  of  each  part,  .80;  Interleaved,  $1.00 

Physician's  Edition.  In  one  volume,  including  the  above  two 
parts,  a  Section  on  Skin  Diseases,  and  an  Index.  6th  Revised 
Edition.  625  pp.  Full  Morocco,  Gilt  Edge,  $2.25 

MURRAY.    Rough  Notes  on  Remedies.    4th  Ed.  $1.25 

TAYLOR.    Practice  of  Medicine.    6th  Edition.  $4.00 

TYSON.  The  Practice  of  Medicine.  By  JAMBS  TYSON,  M.D., 
Professor  of  Medicine  in  the  University  of  Pennsylvania.  A  Com- 
plete Systematic  Text-book  with  Special  Reference  to  Diagnosis  and 
Treatment.  2d  Edition,  Enlarged  and  Revised.  Colored  Plates  and 
125  other  Illustrations.  1222  Pages.  Cloth,  $5.50  ;  Leather,  $6.50 

STOMACH.     INTESTINES. 

FEN  WICK.    Cancer  of  the  Stomach.     Just  Ready.  $3.00 

HEMMETER.  Diseases  of  the  Stomach.  Their  Special  Path- 
ology, Diagnosis,  and  Treatment.  With  Sections  on  Anatomy, 
Analysis  of  Stomach  Contents,  Dietetics,  Surgery  of  the  Stomach, 
etc  sd  Edition,  Revised.  With  15  Plates  and  41  other  Illustrations. 
a  number  of  which  are  in  Colors.  Cloth,  $6.00;  Sheep,  $7.00 


MEDICAL   BOOKS. 


HEMMETER.  Diseases  of  the  Intestines.  Their  Special  Path- 
ology,  Diagnosis,  and  Treatment.  With  Sections  on  Anatomy  and 
Physiology,  Microscopic  and  Chemic  Examination  of  Intestinal 
Contents.  Secretions,  Feces  and  Urine,  Intestinal  Bacteria  and 
Parasites,  Surgery  of  the  Intestines,  Dietetics,  Diseases  of  the 
Rectum,  etc.  With  Full-page  Colored  Plates  and  many  other 
Original  Illustrations.  2  Volumes.  Octavo. 

Price  of  each  Volume,  Cloth,  $5.00;  Sheep,  $5.oo 

SKIN. 

BULKLEY.   The  Skin  in  Health  and  Disease.    Illustrated.    .40 

CROCKER.  Diseases  of  the  Skin.  Their  Description,  Pathol- 
ogy, Diagnosis,  and  Treatment,  with  Special  Reference  to  the  Skin 
Eruptions  of  Children.  3d  Edition,  Thoroughly  Revised.  With 
New  Illustrations.  Just  Ready,  Cloth,  $5.00;  Sheep,  $6.00 

SCHAMBERG.  Diseases  of  the  Skin,  ad  Edition,  Revised  and 
Enlarged.  105  Illustrations.  Being  No.  16  ?  Quiz-Compend  ?  Series. 

Cloth,  .80;  Interleaved,  $1.00 

VAN  HARLINGEN.  On  Skin  Diseases.  A  Practical  Manual 
of  Diagnosis  and  Treatment,  with  special  reference  to  Differential 
Diagno«is.  sd  Edition,  Revised  and  Enlarged.  With  Formulae 
and  60  Illustrations,  some  of  which  are  printed  in  colors.  12.75 

SURGERY  AND  SURGICAL  DIS- 
EASES (see  also  Urinary  Organs). 

BERRY.    Diseases  of  the  Thyroid  Gland.     Illus.  #4.00 

BUTL1N.  Operative  Surgery  of  Malignant  Disease.  2d  Edi- 
tion. Illustrated.  Octavo.  $4-5° 

DAVIS.  Bandaging.  Its  Principles  and  Practice.  163  Original 
Illustrations.  $1.50 

DEAVER.  Surgical  Anatomy.  A  Treatise  on  Human  Anatomy 
in  its  Application  to  Medicine  and  Surgery.  With  about  500  very 
Handsome  full-page  Illustrations  Engraved  from  Original  Drawings 
made  by  special  Artists  from  Dissections  prepared  for  the  purpose. 
Three  Volumes.  Royal  Square  Octavo.  By  Subscription  only. 

Half  Morocco  or  Sheep/  $24.00;  Half  Russia,  $27.00 

DEAVER.  Appendicitis,  Its  Symptoms,  Diagnosis,  Pathol- 
ogy, Treatment,  and  Complications.  Elaborately  Illustrated 
with  Colored  Plates  and  other  Illustrations.  3d  Edition.  Preparing. 

DOUGLAS.  Diagnosis  of  Surgical  Diseases  of  the  Abdomen. 
Illustrated.  In  Press. 

DULLES.  What  to  Do  First  in  Accidents  and  Poisoning. 
5th  Edition.  New  Illustrations.  $1.00 

FULLERTON.     Surgical  Nursing.    3d  Edition.    69  Illus.    $1.00 

HAMILTON.    Lectures  on  Tumors.    3d  Edition.  $J-25 

HEATH.  Minor  Surgery  and  Bandaging.  i2th  Edition,  Revised 
and  Enlarged.  195  Illus.,  Formulae,  Diet  List,  etc.  $1.50 

HEATH.  Clinical  Lectures  on  Surgical  Subjects.  Second 
Series.  .  $2.00 

HORWITZ.  Compend  of  Surgery  and  Bandaging,  including 
Minor  Surgery,  Amputations,  Fractures,  Dislocations,  Surgical  Dis- 
eases, etc.,  with  Differential  Diagnosis  and  Treatment,  sth  Edition, 
very  much  Enlarged  and  Rearranged.  167  Illustrations,  08  Formulae. 

Cloth,  .80;  Interleaved, |i. oo 


24  SUBJECT  CATALOGUE. 

JACOBSON.    Operations    of    Surgery.    4th  Edition,  Enlarged. 

550  Illustrations.  Two  Volumes.  Cloth,  $10.00;  Leather,  $12.00 
KEAY.  Medical  Treatment  of  Gall  Stones.  $1.25 

KEHR.  Gall-Stone  Disease.  Translated  by  WILLIAM  WOTKYNS 

SETMOUR,  M.D.  |2-5o 

MAKINS.  Surgical  Experiences  in  South  Africa.  1899-1900. 

Illustrated.  $4.00 

MAYLARD.  Surgery  of  the  Alimentary  Canal.  97  Illustrations. 

ad  Edition,  Revised.  $3-°° 

MOULLIN.  Text-Book  of  Surgery.  With  Special  Reference  to 

Treatment.     3d  American  Edition.     Revised  and  edited  by  JOHN  B. 

HAMILTON,  M.D.,  LL.D.,  Professor  of  the  Principles  of  Surgery  and 

Clinical  Surgery,  Rush  Medical  College,  Chicago.    623  Illustrations, 

many  of  which  are  printed  in  colors.  Cloth,  £6.00;  Leather,  $7.00 
SMITH.  Abdominal  Surgery.  Being  a  Systematic  Description  of 

all  the  Principal  Operations.  224  Illus.  6th  Ed.  2  Vols.  Clo.,  $10.00 
VOSWINKEL.  Surgical  Nursing.  Second  Edition,  Revised  and 

Enlarged,  in  Illustrations.  $1.00 

WALSHAM.  Manual  of  Practical  Surgery.  7th  Ed.,  Re- 

vised  and  Enlarged.   483  Engravings.  950  pages.  $3-5° 

TEMPERATURE  CHARTS,  ETC. 

GRIFFITH.  Graphic  Clinical  Chart  for  Recording  Temper- 
ature, Respiration,  Pulse,  Day  of  Disease,  Date,  Age,  Sex, 
Occupation,  Name,  etc.  Printed  in  three  colors.  Sample  copies 
free.  Put  up  in  loose  packages  of  fifty,  .50.  Price  to  Hospitals,  500 
copies,  $4.00 ;  1000  copies,  $7.50, 

KEEN'S  CLINICAL  CHARTS.  Seven  Outline  Drawings  of  the 
Body,  on  which  may  be  marked  the  Course  of  Disease,  Fractures, 
Operations,  etc.  Each  Drawing  may  be  had  separately,  twenty-five 
to  pad,  25  cents. 

SCHREINER.  Diet  Lists.  Arranged  in  the  form  of  a  chart. 
With  Pamphlets  of  Specimen  Dietaries.  Pads  of  50.  .75 

THROAT  AND  NOSE  (sec  also  Ear). 

COHEN.    The  Throat  and  Voice.    Illustrated.  .40 

HALL.  Diseases  of  the  Nose  and  Throat,  zd  Edition,  Enlarged. 
Two  Colored  Plates  and  80  Illustrations.  $2.75 

HOLLOPETER.    Hay  Fever.    Its  Successful  Treatment.     $1.00 

KNIGHT.  Diseases  of  the  Throat.  A  Manual  for  Students. 
Illustrated.  Nearly  Ready. 

KYLE  (J.  T.).  Diseases  of  the  Ear,  Nose,  and  Throat.  A 
Compend  Tor  Students.  Illustrated.  In  Press. 

McBRIDE.  Diseases  of  the  Throat,  Nose,  and  Ear.  With  col- 
ored Illustrations  from  original  drawings.  3d  Edition.  $7-°o 

POTTER.  Speech  and  its  Defects.  Considered  Physiologically, 
Pathologically,  and  Remedially.  $1.00 

URINE  AND  URINARY  ORGANS. 

ACTON.  The  Functions  and  Disorders  of  the  Reproductive 
Organs  in  Childhood,  Youth,  Adult  Age,  and  Advanced  Life, 
Considered  in  their  Physiological,  Social,  and  Moral  Relations. 
8th  Edition.  $1.75 


MEDICAL  BOOKS.  25 


HOLLAND.  The  Urine,  the  Gastric  Contents,  the  Common 
Poisons,  and  the  Milk.  Memoranda,  Chemical  and  Microscopi- 
cal, for  Laboratory  Use.  Illustrated  and  Interleaved.  6th  Ed.  £1.00 

KLEEN.    Diabetes  and  Glycosuria.  $2.50 

MEMMINGER.    Diagnosis  by  the  Urine.   2d  Ed.  24  Illus.   fi.oo 

MORRIS.  Renal  Surgery,  with  Special  Reference  to  Stone  in  the 
Kidney  and  Ureter  and  to  the  Surgical  Treatment  of  Calculous 
Anuria.  Illustrated.  $2.00. 

MOULLIN.  Enlargement  of  the  Prostate.  Its  Treatment  and 
Radical  Cure.  2d  Edition.  Illustrated.  $1.75 

MOULLIN.  Inflammation  of  the  Bladder  and  Urinary  Fever. 
Octavo.  $1.50 

SCOTT.  The  Urine.  Its  Clinical  and  Microscopical  Examination. 
41  Lithographic  Plates  and  other  Illustrations.  Quarto.  Cloth,  $5.00 

TYSON.  Guide  to  Examination  of  the  Urine.  For  the  Use  of 
Physicians  and  Students.  With  Colored  Plate  and  Numerous  Illus- 
trations engraved  on  wood.  loth  Edition,  Revised,  Enlarged,  and 
partly  Rewritten.  With  New  Illustrations,  fust  Ready.  $i.£o 

VAN   NUYS.    Chemical  Analysis  of  Urine.    39  Illus. 


VENEREAL  DISEASES. 

GOWERS.    Syphilis  and  the  Nervous  System.  fi.oo 

STURGIS  AND  CABOT.     Student's    Manual    of  Venereal 

Diseases,     yth  Revised  and  Enlarged  Ed.     iamo.  $1-25 


VETERINARY. 

BALLOU.    Veterinary  Anatomy  and  Physiology.    29  Graphic 
Illustrations.  .80;  Interleaved,  $i  .00 


WOMEN,  DISEASES  OF. 

BISHOP.    Uterine  Fibromyomata.   Their  Pathology,  Diagnosis, 
and  Treatment.     Illustrated.  Cloth,  #3.50 

BY  FORD  (H.  T.).    Manual  of  Gynecology.    3d  Edition,  Revised 
and  Enlarged.     363  Illustrations,    fust  Ready.    $3.00  ;  Sheep,  $3.50 

DUHRSSEN.     A  Manual    of  Gynecological    Practice.     105 
Illustrations.  I1 -So 

FULLERTON.     Surgical  Nursing.     3d  Edition,  Revised  and 
Enlarged.     69  Illustrations.  $1.00 

LEWERS.    Diseases  of  Women.    146  Illus.    sth  Ed.  $2.50 

LEWERS.     Cancer  of  the  Uterus,    fust  Ready.  $3.00 

MONTGOMERY.     Practical    Gynecology.     A  Complete  Sys- 
tematic Text- Book.    527  Illustrations.     Cloth,  $5.00;  -Leather,  $6.00 

ROBERTS.      Gynecological    Pathology.     With  127  Full-page 
Plates  containing  151  Figures.  $6.00 

WELLS.    Compend  of  Gynecology.    Illustrated,    ad  Edition. 

.80;  Interleaved,  $i  .00 


"  We  know  ot  no  series  of  books  issued  by  any  house  that  so  fully 
meets  our  approval  as  these  ?  Quiz-Compends  ?.  They  are  well  ar- 
ranged, full,  and  concise,  and  are  really- the  best  line  of  text-books  that 
could  be  found  for  either  student  or  practitioner." — Southern  Clinic. 


BLAKISTON'S  ?  QUIZ-COMPENDS? 

The  Best  Series  of  Manuals  for  the  Use  of  Students. 
Price  of  each,  Cloth,  .80.         Interleaved,  for  taking  Notes,  $1.00. 

These  Compends  are  based  on  the  most  popular  text-books  and 
the  lectures  of  prominent  professors,  and  are  kept  constantly  re- 
vised, so  that  they  may  thoroughly  represent  the  present  state  of  the 
subjects  upon  which  they  treat.  The  authors  have  had  large  experi- 
ence as  Quiz-Masters  and  attaches  of  colleges,  and  are  well  acquainted 
with  the  wants  of  students.  They  are  arranged  in  the  most  ap- 
proved form,  thorough  and  concise,  containing  nearly  1000  illustra- 
tions and  lithograph  plates,  inserted  wherever  they  could  be  used  to 
advantage.  Can  be  used  by  students  of  any  college.  They  contain 
information  nowhere  else  collected  in  such  a  condensed, practical  shape. 

No.  i.  POTTER.  HUMAN  ANATOMY.  Sixth  Edition.  117 
Illustrations  and  16  Plates  of  Nerves  and  Arteries. 

No.  a.  HUGHES.  PRACTICE  OF  MEDICINE.  Part  I.  Sixth 
Edition,  Enlarged  and  Improved. 

No.  3.  HUGHES.  PRACTICE  OF  MEDICINE.  Part  II. 
Sixth  Edition,  Revised  and  Improved. 

No.  4.    BRUBAKER.  PHYSIOLOGY.  Eleventh  Edition.  Illus. 

No.  5.  LANDIS.     OBSTETRICS.     Seventh  Edition.      52  Illus. 

No.  6.  POTTER.  MATERIA  MEDICA,  THERAPEUTICS, 
AND  PRESCRIPTION  WRITING.  Sixth  Revised  Edition. 

No.  7.   WELLS.     GYNECOLOGY.    Second  Ed.     140  Illus. 

No.  8.  GOULD  AND  PYLE.  DISEASES  OF  THE  EYE. 
Second  Edition.  Refraction,  Treatment,  Surgery,  etc.  109  Illus. 

No.  9.  HpRWITZ.  SURGERY.  Including  Minor  Surgery, 
Bandaging,  Surgical  Diseases,  Differential  Diagnosis  and  Treat- 
ment. Fifth  Edition.  With  98  Formulae  and  71  Illustrations. 

No.  10.  LEFFMANN.  MEDICAL  CHEMISTRY.  Fourth 
Edition.  Including  Urinalysis,  Animal  Chemistry,  Chemistry  ot 
Milk,  Blood,  Tissues,  the  Secretions,  etc. 

No.  II.  STEWART.  PHARMACY.  Fifth  Edition.  Based  upon 
Prof.^Remington's  Text- Book  of  Pharmacy. 

No.  ia.  BALLOU.  VETERINARY  ANATOMY  AND  PHY- 
SIOLOGY. 29  graphic  Illustrations. 

No.  13.  WARREN.  DENTAL  PATHOLOGY  AND  DEN- 
TAL MEDICINE.  Third  Edition,  Illustrated. 

No.  14.  HATFIELD.      DISEASES  OF  CHILDREN.    3d  Ed. 

No.  15.  THAYER.     GENERAL  PATHOLOGY.    78  Illus. 

No.  16.  SCH  AMBERG.  DISEASES  OF  THE  SKIN.  Second 
Edition,  Revised  and  Enlarged.  105  Illustrations. 

No.  17.  GUSHING.     HISTOLOGY.     Illustrated.  In  Press. 

No.  18.  THAYER.     SPECIAL  PATHOLOGY.    34  Illustrations. 

No.  19.  KYLE.  DISEASES  OF  THE  EAR,  NOSE,  AND 
THROAT.  Illustrated.  •  In  Press. 


DA  COSTA 


Clinical   Hematology 


A  Practical  Guide  to  the  Examination  of  the  Blood  by 
Clinical  Methods.  With  Reference  to  the  Diagnosis  of 
Disease.  With  Colored  Illustrations.  Cloth,  $5.00 

*.£*  A  new,  thorough,  systematic,  and  comprehensive 
work,  its  purpose  being,  first,  to  show  how  to  examine  the 
blood,  and  second,  how  to  diagnose  from  such  examination 
diseases  of  the  blood  itself  and  general  diseases.  The 
author's  aim  has  been  to  cover  not  alone  the  field  of  original 
research,  but  to  supply  a  book  for  the  student,  the  hospital 
physician  and  the  general  practitioner.  It  will  be  found 
wanting  in  none  of  these  respects. 

OERTEL 


Medical  Microscopy 

JUST  READY 

A  GUIDE  TO  DIAGNOSIS,  ELEMEN- 
TARY LABORATORY  METHODS, 
AND  MICROSCOPIC  TECHNIC 


By  T.  E.  OERTEL,  M.D., 

Professor  of  Pathology  and  Clinical  Microscopy,  Medical  Depart- 
ment, University  of  Georgia. 

WITH  131  ILLUSTRATIONS.    lamo.    Cloth,  $2.00 


JACOBSON'S 
Operations  of  Surgery 


The  Operations  of  Surgery.  By  W.  H.  A. 
JACOBSON,  F.R.C.S.,  Surgeon  to  Guy's  Hospital; 
Consulting  Surgeon  Royal  Hospital  for  Children 
and  Women;  Member  Court  of  Examiners  Royal 
College  of  Surgeons;  Joint  Editor  Annals  of  Sur- 
gery; and  F.  J.  STEWARD,  F.R.C.S.,  Assistant 
Surgeon  Guy's  Hospital  and  to  the  Hospital  for 
Sick  Children.  Fourth  Edition,  Revised,  En- 
larged and  Improved.  550  Illustrations.  Two 
Volumes,  Octavo,  1524  pages.  Cloth,  $10.00 

Sheep,  $12.00 

PRESS  NOTICES  OF  FORMER  EDITIONS 

"  The  author  proves  himself  a  judicious  operator,  as 
shown  by  his  choice  of  methods  and  by  the  emphasis  with 
which  he  refers  to  the  different  dangers  and  complications 
which  may  arise  to  mar  success  or  jeopardize  life." — New 
York  Medical  Record. 

"  The  important  anatomical  points  are  clearly  set  forth, 
the  conditions  indicating  or  contraindicating  operative  inter- 
ference are  given,  the  details  of  the  operations  themselves 
are  brought  forward  prominently,  and  frequently  the  after- 
treatment  is  considered.  Herein  is  one  of  the  strong  points 
of  the  book. " — New  York  Medical  Journal. 
28 


The  Pocket  Cyclopedic  of 
Medicine   and   Surgery 

Full  Limp  Leather,  Round  Corners,  Gilt  Edges,  $1.00 
With  Thumb  Index,  $1.25 

Uniform  -with  "Gould's  Pocket  Dictionary" 


A  concise  practical  volume  of  nearly  600 
pages,  containing  a  vast  amount  of  infor- 
mation on  all  medical  subjects,  including 
Diagnosis  and  Treatment  of  Disease, 
with  Formulas  and  Prescriptions,  Emer- 
gencies, Poisons,  Drugs  and  Their  Uses, 
Nursing,  Surgical  Procedures,  Dose  List 
in  both  English  and  Metric  Systems,  etc. 

By  Drs.  Gould  and  Pyle 

Based  upon  their  large  "Cyclopedia  of 
Medicine  and  Surgery/'  j*  «£*  & 


*#*  This  is  a  new  book  which  will  prove  of  the  greatest 
value  to  students.  It  is  to  the  broad  field  of  general  medi- 
cal information  what  "Gould's  Pocket  Dictionary"  is  to 
the  more  special  one  of  definition  and  pronunciation  of 
words.  The  articles  are  concise  but  thorough,  and  arranged 
in  shape  for  quick  reference.  In  no  other  book  can  be 
found  so  much  exact  detailed  knowledge  so  conveniently 
classified,  so  evenly  distributed,  so  methodically  grouped. 
It  is  Multum  in  Parvo. 

29 


A  NEW  EDITION 

CROCKER  ON  THE  SKIN 

The  Diseases  of  the  Skin.  Their  Description,  Pathology, 
Diagnosis,  and  Treatment,  with  Special  Reference  to  the 
Skin  Eruptions  of  Children.  By  H.  RADCLIFFE  CROCKER, 
M.D.,  Physician  to  the  Department  of  Skin  Diseases,  Uni- 
versity College  Hospital,  London.  With  new  Illustrations. 

Third  Edition,  Rewritten  and  Enlarged 

OCTAVO.    JUST  READY?  CLOTH,  $5.00 


given  the  previous  printings.  The  author  is  a  member  of 
American,  English,  French,  German,  and  Italian  Dermato- 
logical  Societies,  and  a  recognized  authority  the  world  over. 


STURGIS— MANUAL  OF 
VENEREAL  DISEASES 


By  F.  R.  STURGIS,  M.D.,  Sometime  Clinical  Professor  of 
Venereal  Diseases  in  the  Medical  Department  of  the  Uni- 
versity of  the  City  of  New  York.  Seventh  Edition,  Revised 
and  in  Part  Rewritten  by  the  Author  and  FOLLEN  CABOT, 
M.D.,  Instructor  in  Genito-Urinary  and  Venereal  Diseases 
in  the  Cornell  University  Medical  College.  I2mo.  216 
pages.  Cloth,  $1.25 

*#.*  This  manual  was  originally  written  for  students' 
use,  and  is  as  concise  and  as  practical  as  possible.  It  pre- 
sents a  careful,  condensed  description  of  the  commoner 
forms  of  venereal  diseases  which  occur  in  the  practice  of 
the  general  physician,  together  with  the  most  approved 
remedies. 


FOR  THE  DISSECTING-ROOM 

Holden*s  Anatomy — Seventh  Edition 
320  Illustrations 

A  Manual  of  the  Dissections  of  the  Human  Body.  By  JOHN 
LANGTON,  F.R.C.S.  Carefully  Revised  by  A.  HEWSON,  M.D., 
Demonstrator  of  Anatomy,  Jefferson  Medical  College,  Phila- 
delphia, etc.  320  Illustrations.  Two  small  compact  vol- 
umes. I2mo. 

Vol.  I.  Scalp,  Face,  Orbit,  Neck,  Throat,  Thorax,  Upper 
Extremity.  435  pages.  153  Illustrations. 

Oil  Cloth,  $1.50 

Vol.  II.  Abdomen,  Perineum,  Lower  Extremity,  Brain, 
Eye,  Ear,  Mammary  Gland,  Scrotum,  Testes. 
445  pages.  167  Illustrations. 

Oil  Cloth,  $  1. 50 
Each  volume  sold  separately. 


Hughes    ajvd    Keith  —  Dissections 
Illustrated 

A  Manual  of  Dissections  by  ALFRED  W.  HUGHES,  M.B., 
M.R.C.S.  (Edin. ),  late  Professor  of  Anatomy  and  Dean  of 
Medical  Faculty,  King's  College,  London,  etc.,  and  ARTHUR 
KEITH,  M.D.,  Joint  Lecturer  on  Anatomy,  London  Hospital 
Medical  College,  etc.  In  three  parts.  With  527  Colored 
and  other  Illustrations. 

I.     Upper  and  Lower  Extremity.     38  Plates,  1 1 6  other 
Illustrations.  Cloth,  $3.00 

II.     Abdomen,     Thorax.     4    Plates,    149    other   Illus- 
trations. Cloth,  $3.00 
III.     Head,   Neck,  and  Central  Nervous  System.      16 
Plates,  204  other  Illustrations.          Cloth,  $3.00 

Each  volume  sold  separately. 

*.£*  The  student  will  find  it  of  great  advantage  to  have 
a    "Dissector"    to    supplement   his   regular   text-book   on 
anatomy.     These  books  meet  all  requirements,  and  as  they 
can  be  purchased  in  parts  as  wanted,  the  outlay  is  small. 
31 


EDGAR'S 

OBSTETRICS 

A   NEW   TEXT -BOOK 


THE  ILLUSTRATIONS  in  Edgar's  Ob- 
stetrics surpass  in  number,  in  artistic 
beauty,  and  in  practical  worth  those 
in  any  book  of  similar  character.  They 
are  largely  from  original  sources,  are 
made  to  a  scale,  and  have  been  drawn 
by  artists  of  long  experience  in  this 
class  of  medical  work. 
THE  TEXT  has  been  prepared  with 
great  care.  The  author's  extensive  ex- 
perience in  hospital  and  private  prac- 
tice and  as  a  teacher,  his  cosmopolitan 
knowledge  of  literature  and  methods, 
and  an  excellent  judgment  based  upon 
these  particularly  fit  him  to  prepare 
what  must  be  a  standard  work. 

IN      PRESS 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


DEC    2    !« 


939 


LD  21-95m-7,'37 


